This was CNBC's live blog tracking developments on the war in Ukraine.

Four men Russia says were involved in the deadly shootings at a concert hall on the outskirts of Moscow Friday night appeared in court late on Sunday.

The men were charged with committing an act of terrorism when they appeared in the Basmanny district court, accused of carrying out an attack in the Crocus City Hall concert venue in which 137 concertgoers were killed and at least 140 were injured. The Islamic State group has said it was behind the attack.

The suspects, three of whom confirmed as Tajik nationals, appeared in the Basmanny district court late last night, looking disheveled and disoriented. One of the suspects was wheeled into court while another had a bandage removed from his eyes, revealing a black eye.

The suspects, identified as Saidakrami Murodali Rachabalizoda, Dalerdzhon Barotovich Mirzoyev, Shamsidin Fariduni and Muhammadsobir Fayzov, will be detained in custody until May 22, pending trial, the court said on Telegram. They may face life in prison if found guilty.

Three additional suspects have since been detained in regards to Friday's terror attack, according to the courts of general jurisdiction of the city of Moscow. They have been named as Dilovar Isroilovich Islomov, Isroil Ibragimovich Islomov and Aminchon Isroilovich Islomov by the court.

Three further Moscow terror attack suspects detained, Russian court says

Three additional suspects have been detained in regards to Friday's terror attack in Moscow's Crocus City Hall, according to the courts of general jurisdiction of the city of Moscow.

The three men, named as Dilovar Isroilovich Islomov, Isroil Ibragimovich Islomov and Aminchon Isroilovich Islomov, will remain in detention until May 22, 2024 in what the court said via Telegram was a "preventive measure," according to a Google translation.

They have all been accused of committing crimes under Russia's Terrorist Act.

— Sophie Kiderlin

U.S. dismisses Russia linking shooting to Ukraine as "Kremlin propaganda"

The White House on Monday dismissed Russian claims that the shooting attack that killed 137 people in a concert hall outside Moscow was linked to Ukraine.

"There was no linkage to Ukraine. ... This is just more Kremlin propaganda," White House spokesman John Kirby told reporters in a briefing.

— Reuters

France boosts anti-terror unit following Moscow attack

France is increasing the size of its anti-terror unit "Opération Sentinelle," French Prime Minister Gabriel Attal said on Monday, according to Reuters.

Attal said a further 4,000 soldiers will be put on reserve for the unit, which focuses on terror threats and protects places like schools, places of worship and transport hubs. Opération Sentinelle is currently comprised of around 3,000 members of the military.

France on Sunday raised its terror warning to the highest level.

European countries have been considering the threat of terror following the deadly attack in Moscow on Friday night, which the Islamic State group has claimed responsibility for.

— Sophie Kiderlin

Moscow attackers 'deserve no mercy,' Russian prime minister says, amid debate over death penalty

Russia's prime minister told officials Monday that those responsible for the Crocus City Hall terrorist attack on Friday deserved to be shown "no mercy."

Prime Minister Mikhail Mishustin was addressing Communist Party lawmakers Monday, when he commented on the deadly shooting, which he described as a "monstrous terrorist act."

"These events are now being investigated. Those responsible will be punished. They do not deserve mercy," the prime minister said, according to news agency Interfax.

The Islamic State group said it was behind the attack on Friday, which left 137 people dead and 182 injured.

Four men suspected of carrying out the attack were charged with terrorism at a pre-trial hearing in a Moscow court on Sunday evening. Two of the suspects admitted their guilt in the attack, the court said on Telegram, according to a Google translation.

A debate is raging in Russia over whether a moratorium on the death penalty should be lifted, with several prominent lawmakers reportedly arguing for the reintroduction of the punishment for terrorism convictions.

Earlier, Kremlin Press Secretary Dmitry Peskov told reporters that the Kremlin was "not currently taking part in this discussion."

— Holly Ellyatt

Parents of detained Wall Street Journal reporter optimistic over talks for his release

The parents of Wall Street Journal reporter Evan Gershkovich have expressed optimism over the state of government-level talks over his release, as he approaches his one-year anniversary in Russian captivity.

"We have president Biden's promise, delivered to us personally and in the State of the Union [address], and we know that the U.S. government is taking the case very seriously, so we are optimistic," Gershkovich's mother, Ella Milman, said during a televised ABC News interview.

Gershkovich's father, Mikhail, added they were "happy that both governments have expressed willingness to negotiate."

Gershkovich was apprehended by Russian authorities on March 29, 2023, while on assignment in Yekaterinburg. He has been accused, including by Russian President Vladimir Putin, on charges of espionage – which his employer, the Wall Street Journal, vehemently denies.

Putin has previously signaled the possibility of swapping Gershkovich for a Russian prisoner detained abroad, but an agreement has yet to be reached.

 — Ruxandra Iordache

Oil prices rise after Ukrainian strikes on Russian refineries

Crude oil futures rose Monday as Ukraine drone strikes disrupted Russian oil refining capacity.

The West Texas Intermediate contract for April gained 38 cents, or 0.47%, to $81.01 a barrel. The Brent contract for May added 37 cents, or 0.42%, to $85.79 a barrel.

A Ukrainian drone strike caused a fire at the Kuibyshev oil refinery in the city of Samara over the weekend. Industry sources told Reuters that one of the major refining units at the facility was knocked out after the attack.

Kyiv has launched campaign of strikes against Russian energy infrastructure since the start of the year with Ukrainian intelligence claiming a dozen facilities have been successfully hit. At least 10% of Russia's refining capacity has been disrupted by the attacks, according to British intelligence.

— Spencer Kimball

Macron: it would be cynical, counterproductive for Russia to pin Moscow attack on Ukraine

French President Emmanuel Macron said on Monday all signs indicated that Islamic State carried out an attack on a concert hall near Moscow in which 137 people were killed, and he said it would be "cynical and counterproductive" for Russia to blame Ukraine.

Russia has challenged assertions by the United States and other countries that the Islamic State militant group orchestrated Friday's attack, accusing Washington of covering for Ukraine.

"This attack was claimed by Islamic State and the information available to us, to our (intelligence) services as well as to our main partners, indicates indeed that it was an entity of the Islamic State which instigated this attack," Macron said.

"I think that it would be both cynical and counterproductive for Russia itself and the security of its citizens to use this context to try and turn it against Ukraine."

President Vladimir Putin has not publicly mentioned the Islamist militant group in connection with the attackers, who he said had been trying to escape to Ukraine.

Putin said some people on "the Ukrainian side" had been prepared to spirit the gunmen across the border. Ukraine has denied any role in the attack and President Volodymyr Zelenskyy has accused Putin of seeking to divert blame for the attack by mentioning Ukraine.

Russia's foreign ministry spokeswoman, Maria Zakharova, called into question U.S. assertions that Islamic State, which once sought control over swathes of Iraq and Syria, was behind the attack.

— Reuters

Zelenskyy calls for more air defense systems

Ukrainian President Volodymyr Zelenskyy pleaded on Monday for more air defense systems after a ballistic missile attack on the capital, Kyiv.

"Russian terrorists launched ballistic missiles at Kyiv. Unfortunately, houses in a typical urban neighborhood were damaged. As of now, five people have been reported injured. The rubble is being cleared," Zelenskyy said on his Facebook page.

"We reiterate that Ukraine requires more air defense systems, which provide safety for our cities and save lives. All of us who respect and protect life must put an end to this terror," he said.

Russia denies deliberately targeting civilians despite multiple instances of residential buildings and civilian infrastructure being hit in missile and drone attacks.

— Holly Ellyatt

After deadly attack, what could Putin do next?

Russian President Vladimir Putin's next move is being watched closely after he linked Ukraine to the deadly terrorist attack that took place in a Moscow concert hall Friday, leaving at least 137 people dead.

Russian officials and pro-Kremlin hawks continue to level blame at Kyiv for the attack at the Crocus City Hall venue, where gunmen killed concert-goers, including three children, and wounded at least 140.

Kyiv vehemently denies any involvement and Russian authorities are investigating the attack.

Political analysts say that whatever the outcome of that investigation, Putin is likely to use the tragedy to his advantage as he looks to boost domestic support for the war in Ukraine and to "advance its broader geopolitical objectives," as one analyst put it.

Read more on the story here: Putin expected to use deadly Moscow attack to Russia’s advantage, whoever’s to blame

Two ballistic missiles destroyed over Kyiv, air force says

Ukraine's air force said two ballistic missiles had been destroyed over the capital Kyiv Monday morning.

"TWO BALLISTIC MISSILES DESTROYED," the air force posted on Telegram, attributing the comments to Air Force Commander Lieutenant General Mykola Oleschuk.

"Around 10:30 am, the enemy attacked Kyiv with two ballistic missiles from the temporarily occupied Crimea. Targets destroyed." CNBC was unable to verify the information in the update.

— Holly Ellyatt

Ukraine keeps power imports high, sees no exports after Russian strikes

Ukraine is keeping electricity imports high and not planning to export power on Monday after Russian attacks on the energy sector, the energy ministry said.

Russia attacked Ukrainian generating and transmission facilities last week and over the weekend, causing blackouts in many regions.

"For the current day, electricity imports are forecast at 14,887 megawatt hours (MWh). No exports are expected," the ministry said in a statement.

Ukraine imported 14,900 MWh on Sunday and 3,300 MWh a day before the first in the latest wave of attacks on its power sector on March 22.

Emergency power outages were introduced in Ukraine's port of Odesa on Monday after a Russian air attack damaged one of the high-voltage facilities there, Ukraine's top energy provider DTEK said in a separate statement.

It said that to reduce the load on the network electric transport would not operate in the city and industrial consumption was also limited.

The Ukrainian military says air defences destroyed eight out of nine drones launched by Russia overnight. Most of the drones were destroyed in the Odesa and Mykolaiv regions.

Debris from a falling drone sparked a fire at a power facility, which was promptly put out, the Odesa city administration said.

"The enemy has started systematically hitting the city's energy infrastructure. The situation is bad. They're hitting civilian targets," Mykolaiv's governor Vitaly Kim told national television.

— Reuters

Russia will not comment on Islamic State group's claim of terror attack, Kremlin spokesperson says

A Russian investigation into the deadly shootings at the Crocus concert hall on Friday is ongoing, and the Kremlin is not commenting on the involvement of the Islamic State group, spokesperson Dmitry Peskov said Monday.

In Google-translated comments carried by Russian state news agency Tass, he added that Russian special services are working independently on the probe and that there is no discussion of help from foreign countries.

At least 137 people were killed in the attack, and another 97 who were injured remain hospitalized, Moscow Governor Andrey Vorobyov said in separate Google-translated comments reported by Tass.

The Islamic State group has claimed responsibility for the attack. Russian President Vladimir Putin raised the possibility of Ukrainian involvement in the shootings — which Kyiv denies. Four men Moscow claims were involved in the terror attack appeared in court late on Sunday.

— Ruxandra Iordache

Ukraine foreign minister calls for further air defense support after missile attack on Kyiv

Ukrainian Foreign Minister Dmytro Kuleba said on Monday that an attempted Russian ballistic missile strike on Kyiv underscored the urgent need for more air defense support.

In a social media post on X, Kuleba posted a video of children in Ukraine's capital running for cover as Russian missiles were shot down over the capital. CNBC could not independently verify the video nor developments on the ground.

"This is a reminder that Ukraine urgently requires more air defense, particularly Patriot systems and missiles capable of repelling any Russian attack," Kuleba said.

Ukrainian officials had earlier reported explosions in Kyiv, along with debris falling in several districts of the capital.

U.S. ambassador to Ukraine Bridget Brink said Russia attacked Ukraine's capital with hypersonic missiles on Monday morning, adding "there is not a moment to lose" in providing further assistance to Ukraine.

"Loud explosions in Kyiv," Brink said via X on Monday. "Over the last 5 days, Russia has launched hundreds of missiles and drones against a sovereign country," she added.

— Sam Meredith

Photos show a memorial gathering in the Russia-controlled city of Donetsk

Photos published via Getty Images show people gathering at a memorial service on Sunday in the Russia-controlled city of Donetsk in eastern Ukraine.

Russia on Sunday observed a national day of mourning after deadly shootings at the Crocus City Hall on the outskirts of Moscow on Friday evening. At least 137 people were killed in the attack.

— Sam Meredith

Explosions rock Kyiv

Ukrainian officials reported explosions erupting in Kyiv on Monday morning, along with debris falling in several districts of the capital city.

A multi-story building sustained damage in the Pechersk district as the result of a missile attack, while debris has fallen in the Solomyansk and Dnipro districts, according to a Google-translated Telegram update from the Kyiv military administration.

Kyiv Mayor Vitali Klitschko said emergency services were called to attend at the site of the two districts and in Dniprovskyi, after reporting explosions in the capital city earlier in the day, in two separate Google-translated Telegram posts.

CNBC could not confirm developments on the ground.

— Ruxandra Iordache

Eleven injured in Mykolaiv as fire erupts after drone collapse

Eleven people were injured, as fire broke after the collapse of a downed drone in the Mykolaiv region in southern Ukraine, according to the country's state emergency service.

It added that two of the injured were hospitalized in the Sunday night attack. No casualties were reported.

In a Google-translated update on Telegram, the agency said that a two-story residential building was destroyed as a result of the debris, while nearby houses were damaged by a blast wave.

In a separate Google-translated post on social media platform X, the general staff of Ukraine's armed forces said Ukrainian factions shot down eight out of nine Russian-deployed "Shahed" missiles in the Mykolaiv and Odesa regions.

CNBC could not independently verify the reports.

— Ruxandra Iordache

At least 200,000 users without power in Kharkiv and nearby regions after Russian strikes, Ukrainian officials say

More than 200,000 electricity consumers in Kharkiv city and a regional district are without stable power supply following Russian strikes, Ukrainian President Volodymyr Zelenskyy said in his nightly address on Sunday.

Oleh Sinegubov, head of the Kharkiv regional state administration, confirmed the number of disconnected electricity subscribers in a Google-translated update on Telegram, adding that a schedule of power outages is in effect at Kharkiv and eight regional communities.

Zelenskyy separately assessed that Russian forces deployed 190 missiles and nearly 140 Iranian-make Shahed drones against Ukraine over the last week, as well as launched almost 700 guided aerial bombs.

CNBC could not independently verify these reports.

— Ruxandra Iordache

Putin's focus on Ukraine may leave Russians exposed to real security risks, foreign policy fellow warns

Russian leader Vladimir Putin's hyper focus on Ukraine could expose Russians to more security threats, warns Maximilian Hess, fellow at the Foreign Policy Research Institute.

Hess' comments come after a terrorist attack at a concert hall in Moscow left more than 130 people dead, according to Reuters. Islamic State terrorist group said it was behind the attack. Russian forces have stressed a potential link between the responsible gunmen and Ukraine, while Kyiv denies any involvement.

"Putin is so obsessed with this conflict in Ukraine that I think he's going to focus his security response there and use this, essentially, as an excuse to try to build up that narrative," Hess told CNBC's "Capital Connection," stressing that the "whole security apparatus has been focused on Russia's war in Ukraine."

He noted that the Islamic State has previously carried out attacks in Moscow and St. Petersburg and may be motivated by Moscow's operations in Syria.

"What's interesting though is that Putin doesn't seem to be focusing on that aspect of it. He's very much trying to blame Ukraine for this attack. There's no evidence of Ukrainian involvement, it doesn't fit in line with the types of attacks that Kyiv has carried out in the past, including ongoing," Hess said. "That will itself leave Russians less secure, because he's focusing on a non-real security risk."

— Ruxandra Iordache

Moscow attack suspects appear in court

Four men Russia says were involved in the deadly shootings at a concert hall on the outskirts of Moscow Friday night appeared in court late on Sunday.

The men, three of whom confirmed as Tajik nationals, were charged with committing an act of terrorism when they appeared in the Basmanny district court late last night. They're accused of carrying out an attack in the Crocus City Hall concert venue in which 137 concertgoers were killed and at least 140 were injured.

The suspects, identified as Saidakrami Murodali Rachabalizoda, Dalerdzhon Barotovich Mirzoyev, Shamsidin Fariduni and Muhammadsobir Fayzov, will be detained in custody until May 22, pending trial, the court said on Telegram. The suspects may face life in prison if found guilty, the RIA Novosti news agency reported.

One of the suspects was brought into court in a wheelchair while another had a bandage removed from his face, revealing a black eye. Another appeared dazed and disoriented, video footage of the suspects released by the court showed.

— Holly Ellyatt

Russian power plant units shut down after fire, governor says

Two units at the Novocherkassk thermal power plant in Russia's southwestern Rostov region were shut down early Monday morning after a fire, the region's governor said.

"Due to the fire, the 330 kV high-voltage lines — Tikhoretskaya and Rostovskaya — were automatically switched off," Rostov Governor Vasily Golubev said on Telegram.

It's unclear whether the fire at the plant was linked to a purported Ukrainian drone attack against the region overnight; Russia's Defense Ministry said on Telegram that its forces had intercepted 11 Ukrainian drones over Rostov.

CNBC could not independently verify the report and Ukraine has not commented on the attacks.

— Holly Ellyatt

Emergency power shutdowns in Ukraine's Odesa after Russian attack

Emergency power outages were introduced in Ukraine's port of Odesa on Monday after a Russian air attack damaged one of the high-voltage facilities there, Ukraine's top energy provider DTEK said on Monday.

"The situation remains difficult," DTEK said on the Telegram messaging app. "In order to reduce the load on the network, electric transport will not operate in the city today, and industrial consumption is also limited."

The administration of Odesa said on Telegram that the city and the region were attacked by several waves of drones launched by Russia. Four of the air weapons were shot down over the Odesa and neighbouring Mykolaiv regions.

Debris from a falling drone sparked a fire at the power facility, which was promptly put out, the administration added.

DTEK said power was restored by Monday morning to two city districts.

— Reuters