Police and rescue crews sifted through the rubble of a mosque and dozens of flattened mud-brick homes on Sunday looking for survivors of the worst attack in Iraq this year — a truck bombing blamed on Al Qaeda that killed 72 people.

Political parties said Saturday's attack against a Shiite mosque near the ethnically tense city of Kirkuk aimed at destabilizing Iraq, which is slowly trying to return to normal after years of ethnic and religious bloodletting.

The bombing, which wounded 163 people, came as U.S. troops have been withdrawing from Iraqi cities as part of a security agreement that requires all troops to leave the country by the end of 2011. There are concerns that violence will spike after U.S. troops fully pull out of the cities by a June 30 deadline.

Prime Minister Nouri al-Maliki has called for calm and said there will be no delay in the U.S. withdrawal. He warned over the weekend that there could be attempts to destabilize the country.

Police Brig. Gen. Sarhat Qadir said the death toll from Saturday's attack was so high because most of the 30 homes that were damaged around the mosque were made of mud. The mosque was flattened.

"The operation has Al Qaeda fingerprints," he said, adding that an investigation was ongoing. There were conflicting reports about whether the attack was carried out by a homicide bomber or if the truck was booby-trapped.

It took place in Taza, 10 miles south of Kirkuk, which is home to about 20,000 people — many of them Shiites from the Turkomen minority.

"It is a quiet town, but Al Qaeda targeted it to try to ignite the sectarian sedition in Iraq," said Tahseen Kahaya, a member of the Islamic Turkomen party.

Sunni insurgents and terror groups such as Al Qaeda remain active in northern Iraq despite security gains around the country. Tensions have also spiked in the oil-rich area as Kurds seek to incorporate Kirkuk into their semiautonomous region despite opposition by Arabs, Turkomen and other rival ethnic groups.

"There are groups working to inflame the situation in Kirkuk, which cannot be solved without calm and constructive dialogue," the Sunni Iraqi Islamic Party said. It blamed the attack on the "the enemies of Iraq and their agents who do not wish to see Iraq as a stable and calm country."

Although violence has dropped sharply in Iraq, daily attacks continue. In northern Mosul, a roadside bomb targeting a police patrol on Sunday killed a bystander and wounded three others, police said.

According to an Associated Press count, at least 1,678 Iraqis, civilians and security personnel have been killed since Jan. 1. Although the figure is lower than the 4,809 who died from attacks in the first six months of last year, there have been at least 19 bombings that killed more than a dozen people so far this year.