An Iraqi Army armored vehicle is seen outside the Abu Hanifa mosque in the Azamiyah neighborhood of north Baghdad, Iraq after Iraqi troops raided the mosque on Monday, Aug. 6, 2007. Acting on tips from local residents, a US military statement said, Iraqi soldiers searched the mosque and uncovered a sizeable cache of weapons in the courtyard. [AP]

Meanwhile, a suicide bomber killed at least 28 people in a northern city, including 19 children, some playing hopscotch and marbles in front of their homes. And the American military reported five new US deaths: Four soldiers were killed in a combat explosion in restive Diyala province north of the capital Monday, and a soldier was killed and two were wounded during fighting in eastern Baghdad on Sunday.

The new cracks in Prime Minister Nouri al-Maliki's government appeared even as US military officials sounded cautious notes of progress on security, citing strides against insurgents linked to al-Qaida in Iraq but also new threats from Iranian-backed Shiite militias.

Despite the new US accusations of Iranian meddling, the US and Iranian ambassadors met Monday for their third round of talks in just over two months. A US embassy spokesman called the talks between US Ambassador Ryan Crocker and his counterpart, Hassan Kazemi Qomi, "frank and serious."

But it was al-Maliki's troubles that seized the most attention.

The Cabinet boycott of five ministers loyal to former Iraqi leader Ayad Allawi left the government, at least temporarily, without participants where were members of the Sunni political apparatus - a deep blow to the prime minister's attempt to craft reconciliation among the country's majority Shiites and minority Sunnis and Kurds.

The defense minister is from a Sunni background but has no political ties and was chosen by al-Maliki.

The Allawi bloc, a mixture of Sunnis and Shiites, cited al-Maliki's failure to respond to its demands for political reform. The top Sunni political bloc already had pulled its six ministers from the 40-member Cabinet of al-Maliki, a Shiite, last week.

Iraqi President Jalal Talabani, who has been trying to broker the Sunni bloc's return in a bid to hold the government together, met Monday with Crocker and a White House envoy.

In Washington, State Department spokesman Sean McCormack said the United States was working well with the al-Maliki government, but he did not give the kind of enthusiastic endorsement that President Bush and his aides once did.

"There's a very healthy political debate that is going on in Iraq, and that is good," McCormack said. "It's going to be for them (the Iraqi people) to make the judgments about whether or not that government is performing."

Lawmaker Hussam al-Azawi, of the bloc loyal to Allawi, said the boycott began with Monday's Cabinet meeting. The ministers intend to continue overseeing their ministries.

"We demanded broader political participation by all Iraqis to achieve real national reconciliation ... and an end to sectarian favoritism," al-Azawi said.

Meanwhile, Iraqi authorities girded for a major Shiite pilgrimage later this week in Baghdad with plans to tighten security.

Sunni insurgents often target such gatherings. And this particular annual march, to commemorate the eighth-century death of a key Shiite saint, was struck by tragedy in 2005, when thousands of Shiite pilgrims, panicked by rumors of a suicide bomber, broke into a stampede on a bridge, killing 1,000.

Brig. Gen. Qassim al-Moussawi, an Iraqi military spokesman for Baghdad, said the government was considering a driving ban during the march this week, but had not made a decision.

However, Iraqi security forces will intensify checkpoints and marchers will be banned from carrying weapons, cell phones or even bags, he said.

In Tal Afar to the north, officials slapped an immediate curfew on the religiously mixed city after a suicide bomber slammed his truck into a crowded Shiite neighborhood. The blast killed at least 28 people, including at least 19 children, according to Brig. Gen. Najim Abdullah, who said the dump truck was filled with explosives and covered with a layer of gravel.

The powerful Monday morning blast caused houses to collapse as many families were getting ready for the day ahead, and officials said the death toll could rise.

Several residents said boys and girls were playing hopscotch and marbles outside the houses at the time of the explosion.

"This is an ugly crime. I cannot understand how the insurgents did not think about these children," said one man, Kahlil Atta, a wedding photographer in the city.

Tal Afar, which was cited by Bush last March as a success story after major military operations against insurgents, has been the frequent site of Sunni extremist attacks in the past year.

Elsewhere, 60 decomposing bodies were found in a mainly Sunni area that had been under the control of al-Qaida in Iraq west of Baqouba, according to a Diyala police official. The US military said it had no information about any discovery.

At least 53 other people were killed or found dead elsewhere in Iraq, according to police. Those included the bodies of five soldiers who had been ambushed by gunmen while on their way home for vacation north of Tikrit.

All Iraqi police officials spoke on condition of anonymity because they were not authorized to release information.

The Iranian talks come as the US military steps up accusations that Tehran is arming and training Shiite militants to attack American forces in Iraq.

Lt. Gen. Raymond Odierno, the US second-in-command, said Sunday that rogue Shiite militiamen with Iranian weapons and training launched 73 percent of the attacks that killed or wounded American forces last month in Baghdad, nearly double the figure six months earlier.

Tehran has denied US allegations that it is fueling violence in Iraq.

On Monday, the Iranian delegation criticized what it called America's "suspicious" security approach toward Iraq, according to the Islamic Republic News Agency. It called for "a change in the broad policies and approach of the US"