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

Russia and Ukraine traded retaliatory strikes over the weekend after another Russian oil terminal was attacked on Sunday, as were the Russian-occupied city of Donetsk and nine Ukrainian regions.

Moscow accused Kyiv of launching a missile strike on a market in Donetsk city, killing at least 25 people and wounding 20 others, Russian officials said. Ukrainian armed forces operating in the region denied they had carried out the strike, stating that they "did not conduct any combat operations with means of destruction."

Elsewhere, a fire broke out at a terminal of Russia's largest liquefied natural gas producer Novatek on the Baltic Sea, a regional official said on Sunday, amid reports of drone sightings in the area. Several other Russian oil terminals have been targeted in recent days, in the Bryansk and Leningrad regions.

Meanwhile, Ukrainian President Volodymyr Zelenskyy said Russian forces shelled nine regions in the country on Sunday.

Zelenskyy thanks Poland for 'new defense package'

Ukrainian President Volodymyr Zelenskyy announced a "new Polish defense package" after meeting in Kyiv with Poland's Prime Minister Donald Tusk, who was making his first visit to a non-EU country since returning to the top job in December.

"We appreciate such unflagging support. There is a new form of our cooperation – aimed at a larger scale of arms purchases for Ukrainian needs – the Polish loan for Ukraine," Zelenskyy said in a statement.

Further details of the defense package were not provided. CNBC has contacted the Polish Ministry of Foreign Affairs for comment.

The leaders also discussed "the possibilities of joint future arms production," Zelenskyy said.

Tusk, the former president of the European Council, meanwhile said that Poland would try to help Ukraine with its process of EU accession.

It comes as the neighboring countries vow to end an ongoing and heated dispute over cross-border trade flows. Political relations deteriorated in fall 2023, leading to then-Prime Minister Mateusz Morawiecki saying Poland would no longer supply weapons to Ukraine.

— Jenni Reid

Poland and Ukraine pledge quick end to political friction

The leaders of Poland and Ukraine pledged on Monday to tackle a thorny political dispute that had hampered their critical wartime alliance and boost defence cooperation as Russia's invasion grinds towards its third year.

In his first visit to neighbouring Ukraine as prime minister, Poland's Donald Tusk delivered a message of friendship to President Volodymyr Zelenskyy and said both sides "have reached a common understanding" over protests by Polish truckers.

"Poland will do everything to increase Ukraine's chances of victory in this war," Tusk said at a joint media briefing.

Warsaw became a key ally for Kyiv as it sought Western financial and military support against Russia, but relations deteriorated in recent months when blockades at the border damaged Ukraine's economy.

The truckers agreed last week to suspend their protests, which had been aimed at revoking Ukrainian truckers' permit-free access to the European Union, until March 1.

"We understand the depth of the reasons that led to this kind of situation, but draw attention first and foremost to the depth of the threat that stands before our peoples," Zelenskyy said, adding that he welcomed Warsaw's work on the issue.

Both leaders hailed plans between their countries for joint arms production and Zelenskyy said on X that they had discussed "a new form of cooperation aimed at larger-scale arms purchases for Ukrainian needs". He did not give details.

— Reuters

Death, injury toll rises after Donetsk market attack

The number of people killed or injured in a missile strike on a market in Donetsk city on Sunday has risen, a Russian-installed official said Monday.

Denis Pushilin, head of the separatist Donetsk People's Republic, told the Rossiya-24 news channel that 27 people have now died in the strike, and 26 are injured, news agency RIA Novosti said, reporting his comments.

Pushilin blamed the attack on Ukraine, saying it had resorted to targeting civilians as a result of failures on the battlefield.

"The methods do not change: the worse the enemy's situation within the military confrontation, the more often they try to take it out on the civilian population. Non-humans. We see a dependence here in the sense that the enemy's capabilities become fewer, and as soon as such an opportunity arises, they try take it out on the civilian population," he claimed.

Pushilin also claimed Ukraine had used cluster munitions in the strike, which the Kremlin described as a terrorist attack.

Ukrainian armed forces operating in the region denied they had carried out the attack, stating Sunday that they "did not conduct any combat operations with means of destruction."

A day of mourning in Donetsk was declared by Russian authorities Monday.

— Holly Ellyatt

Ukraine's Zelenskyy hails diaspora's support, proposes dual citizenship

President Volodymyr Zelenskyy thanked Ukrainians abroad on Monday for their support during Russia's invasion, and proposed changing the constitution to allow dual citizenship.

Ukraine's constitution does not give Ukrainian citizens the right to dual citizenship, so millions of people of Ukrainian origin who live abroad are unable to hold Ukrainian passports.

In what appeared a symbolic gesture on Ukraine's Unity Day, marking the anniversary of the unification of eastern and western Ukraine in 1919, Zelenskyy said he was submitting draft legislation to parliament that would allow dual citizenship.

"Today I am submitting to the Verkhovna Rada a key draft law that will allow the adoption of comprehensive legislative amendments and the introduction of multiple citizenship," Zelenskyy said in a statement.

"And it will allow all ethnic Ukrainians and their descendants from around the world to have our citizenship. Of course, except for citizens of the aggressor country."

Ukrainian officials often refer to Russia as the aggressor country following its full-scale invasion on Feb. 24 2022 and occupation of swathes of Ukrainian territory. Zelenskyy has frequently underlined the need for unity as Russia's war in Ukraine drags on, with Kyiv heavily dependent on military and financial aid from abroad.

Thanking the diaspora for its support, including those who had come to fight for Ukraine, Zelenskiy said the words "I am Ukrainian" carried a special meaning, and hailed the "indomitability of our people."

Changes to the constitution need the approval of parliament, a process that could take about a year, and the authorisation of the Constitutional court.

— Reuters

Kremlin calls Donetsk market strike a 'monstrous act of terrorism'

The Kremlin called the alleged Ukrainian shelling of a marketplace in Donetsk Sunday a "monstrous act of terrorism."

"The Kyiv regime continues to show its bestial face and strikes at civilians," Kremlin Press Secretary Dmitry Peskov told reporters Monday.

At least 25 people died in the attack on the market in Donetsk city, while 20 others were injured.

Ukrainian armed forces operating in the region denied they had carried out the strike, stating that they "did not conduct any combat operations with means of destruction."

Russia claims Donetsk in eastern Ukraine as its own territory, having unilaterally annexed the region in late 2022. Ukraine and its allies reject the claim.

Peskov added on Monday that Russian President Vladimir Putin had received reports on the Donetsk attack and that Russia's "special military operation" — as it calls its invasion of Ukraine — would continue in order to "protect" people.

— Holly Ellyatt

Operations at damaged Russian fuel complex seen resuming within weeks, say analysts

Russian energy company Novatek is likely to resume large-scale operations at its Ust-Luga processing complex and Baltic Sea terminal within weeks, following a suspected drone attack seen disrupting naphtha flows to Asia, analysts said on Monday.

The tightening of supply from Russia, following fears of disruption in European naphtha exports to Asia from Yemeni Houthis' attacks on ships in the Red Sea, are driving up naphtha prices and refining margins in Asia.

The profit margin for making naphtha in Asia jumped by about $6 to $91.70 per metric ton over Brent crude on Monday after four straight sessions of losses.

Novatek said on Sunday it had been forced to suspend some operations at the huge Baltic Sea fuel export terminal and "technological process" at the complex due to a fire, started by what Ukrainian media said was a drone attack.

Kommersant newspaper also said on Monday, citing local authorities, that two storage tanks and a pumping stations were damaged due to the incident.

"We believe the plant is likely to return to significant capacity within weeks or, at worst, months," analysts at Moscow-based BCS brokerage said in a note.

Novatek declined to comment. Kremlin spokesman Dmitry Peskov said on Monday that Russia's military and other government agencies were taking the necessary measures, including when it comes to air defences, after the suspected Ukrainian drone attack on the terminal.

— Reuters

Russia declares a day of mourning Monday for victims of market attack

A day of mourning has been declared Monday for the victims of Sunday's shelling of a marketplace in the Russian-occupied city of Donetsk.

Moscow accused Kyiv of launching a missile strike on the market in Donetsk, killing at least 25 people and injuring 20 others, and described the incident as a terrorist attack.

Ukrainian armed forces operating in the region denied they had carried out the strike, stating Sunday that they "did not conduct any combat operations with means of destruction."

Both Russia and Ukraine deny the deliberate targeting of civilians, although thousands have died in missile and drone strikes over the last two years of war.

The Russia-installed head of Donetsk, Denis Pushilin, said on Telegram Monday that there would be a day of mourning for the dead.

"We mourn those who died at the hands of Ukrainian terrorists as a result of yesterday's shelling," he said.

Pushilin, the head of the self-proclaimed, pro-Russian "Donetsk People's Republic," said the strike had been carried out "on Sunday, when it is most crowded there."

Russia said the Ukrainian forces' strike on Donetsk will be discussed at a U.N. Security Council meeting on Monday. "The Russian Foreign Ministry called on all responsible governments and international structures to condemn this terrorist attack," news agency Tass reported.

— Holly Ellyatt

Russian offensive activity increasing in intensity, UK says

Russian offensive activity is increasing in intensity, data collected by Ukraine's armed forces in mid-January confirms, Britain's Ministry of Defense said Sunday.

Ukraine's General Staff reported Friday that there was a 27% rise in Russian assaults on the front line over the previous day, with 81 air strikes and 45 multiple rocket attacks.

It's a trend that has been emerging since the new year, according to additional data that's been collected, the U.K. noted in an intelligence update on X.

"This data points towards a steady increase in the intensity of Russian offensive activity across the front over the past two weeks. A key enabler for this is highly likely the freezing ground conditions, which allows cross-country movement of armoured vehicles," it noted.

Data from the Ukrainian General Staff compared the period of January 14-18 with the previous five-day period. It showed a trend of increased losses for Russia as offensive activity ticked up.

"Over these five-day periods the number of military vehicle losses by Russia increased by 88% and the number of Russian tank losses increased by 95%. The number of Russian casualties over the same period also increased by 15%," the ministry noted.

— Holly Ellyatt

Russia and Ukraine trade retaliatory strikes over the weekend

Russia and Ukraine traded retaliatory strikes over the weekend after another Russian oil terminal was attacked on Sunday, as were the Russian-occupied city of Donetsk and nine Ukrainian regions.

Moscow accused Kyiv of launching a missile strike on a market in Donetsk city, killing at least 25 people and wounding 20 others, Russian officials said. Ukrainian armed forces operating in the region denied they had carried out the strike, stating that they "did not conduct any combat operations with means of destruction."

Elsewhere, a fire broke out at a terminal of Russia's largest liquefied natural gas producer Novatek on the Baltic Sea, a regional official said on Sunday, amid reports of drone sightings in the area. Several other Russian oil terminals have been targeted in recent days, in the Bryansk and Leningrad regions.

Meanwhile, Ukrainian President Volodymyr Zelenskyy said Russian forces shelled nine regions in the country on Sunday.

"In this single day, the Russian inhumans shelled over a hundred cities, towns, our Ukrainian villages in nine regions: from the Chernihiv region to the Sumy region, Mykolaiv region, Kirovohrad region, our regions. Particularly severe Russian strikes are in the Donetsk region," Zelenskyy said in his nightly address.

Describing 60 clashes yesterday, Zelenskyy said the most intense fighting was in the Avdiivka area, as well as in Bakhmut, Maryinka and Kupiansk. "There have been more than 50 Russian shelling incidents just from multiple rocket launcher systems, and also dozens of airstrikes and missile strikes," he said.

Both Russia and Ukraine deny targeting civilian infrastructure. CNBC was unable to immediately verify the battlefield reports.

— Holly Ellyatt

Fire erupts at Russia’s Novatek Baltic Sea terminal after suspected Ukrainian drone attack

A fire broke out at a Baltic Sea terminal belonging to Novatek, Russia's largest liquefied natural gas producer, after a suspected Ukrainian drone attack, forcing the company to suspend some operations there.

The Ust-Luga complex, located on the Gulf of Finland about 170 km (110 miles) west of St. Petersburg, processes stable gas condensate into light and heavy naphtha, jet fuel, fuel oil and gasoil, according to Novatek's website. The port is used to ship processed products to international markets.

The Interfax-Ukraine news agency, citing unnamed sources, said the fire was the result of a special operation carried out by Ukraine's security services.

"The Ust-Luga Oil terminal in the Leningrad region is an important facility for the enemy. Fuel is refined there, which, among other things, is also supplied to Russian troops," it cited one source as saying.

"A successful attack on such a terminal not only causes economic damage to the enemy, depriving the occupiers of the opportunity to earn money to wage war in Ukraine, but also significantly complicates the logistics of fuel for the Russian military."

Reuters could not confirm that the fire resulted from a Ukrainian drone attack.

— Reuters

Zelenskyy worried by the prospect of Trump presidency

Ukrainian President Volodymyr Zelenskyy said he was worried by the prospect of Donald Trump returning to the White House, branding Trump's claim that he could stop Ukraine's war with Russia in 24 hours as "very dangerous."

In an interview with the U.K.'s Channel 4 News that aired Friday, Zelenskyy invited the former president and front-runner for the Republican presidential nomination to visit Kyiv, but only if Trump delivers on his promise.

"Donald Trump, I invite you to Ukraine, to Kyiv. If you can stop the war during 24 hours, I think it will be enough to come," Zelenskyy said.

The Ukrainian leader also shared his concern about the U.S. taking unilateral action that failed to consider Ukraine's perspective, noting the dearth of details around Trump's "peace plan."

— Associated Press