The blast near Kirkuk — a city rife with ethnic tensions — came hours after the prime minister warned Iraqis to expect more violence as U.S. troops withdraw from Iraqi cities by the end of this month, but he insisted the deadline will be met "no matter what happens."
The Americans already have begun pulling back combat troops from inner-city outposts in Baghdad, Mosul and other urban areas ahead of the June 30 deadline set in a security pact that calls for a full U.S. withdrawal from Iraq by 2012.
But continued assassinations and high-profile explosions have heightened concerns that Iraqi forces are not ready to take over their own security.
Police Brig. Gen. Sarhat Qadir said Sunday that the attack was not a suicide bombing but that the "operation has al-Qaida finger prints."
Worshippers were leaving the mosque in Taza, 10 miles south of Kirkuk, following noon prayers when the truck exploded, demolishing the mosque and several mud-brick houses across the street, according to police and witnesses.
Rescue teams searched into the night to find people buried under the rubble while women begged police to let them near the site so they could search for loved ones. The U.S. military said it was providing generator lights and water at the site.
Ambulances rushed victims to the overwhelmed hospital in Kirkuk and some victims had to be taken to nearby cities. Three babies cried as they were placed on a single hospital bed to be treated.
The death toll rose to at least 72 as more bodies were found beneath the debris, according to police and hospital officials, who spoke on condition of anonymity because they weren't authorized to release the information.
Brig. Gen. Sarhat Qadir of the Kirkuk police force said earlier that at least 63 people were killed and 170 were wounded, but he expected the number to rise.
Witnesses said the truck was parked across the street from the mosque and they assumed the driver was praying, although Kirkuk's police chief, Maj. Gen. Jamal Tahir, said investigators were looking into the possibility it was a suicide bombing.
"The truck was parked near our house; therefore most of the victims were found beneath the debris of the houses, mostly women and children," said Ehsan Mushir Shukur, whose sister was seriously wounded and taken to the Kurdish city of Sulaimaniyah.
He said his wife was also wounded while his sister's young son and daughter were killed.
Yellman Zain-Abideen, who was wounded by shrapnel in his hand and face, cried for his missing son who had been leaving the mosque with him when the blast occurred.
He blamed local authorities for not providing sufficient security in the mainly Turkomen area, which is surrounded by Sunni villages.
"There should have been guards around the mosque, we are living in an area surrounded by enemies," he said.
AP Television News footage later showed men using pickaxes and shovels to dig dozens of graves in the cemetery behind the mosque to bury the victims.
Many of the town's residents had fled to neighboring Iran under Saddam Hussein's Sunni-dominated regime but returned following the 2003 U.S.-led invasion. The area is a stronghold of supporters of Prime Minister Nouri al-Maliki's Shiite Dawa party as well as the powerful Shiite Supreme Islamic Iraqi Council.
Nobody claimed responsibility for the attack, but it bore the hallmark of al-Qaida in Iraq or other Sunni insurgents who remain active in northern Iraq despite security gains.
Tensions have risen in the oil-rich area as Kurds seek to incorporate Kirkuk into their semiautonomous region despite opposition from Arabs, Turkomen and other rival ethnic groups.
Officials also have warned that insurgents are likely to stage more attacks after the withdrawal deadline to try to undermine confidence in the government's ability to protect its people.