BAGHDAD (AP) – Four more American soldiers were killed in roadside bombings in the Baghdad area, including three in a single strike, the military said Tuesday, raising to at least 19 the number of troop deaths in the first week of August.

The numbers signaled a resurgence in attacks after July saw the lowest number of American casualties in eight months. American commanders have warned they expected militants to try to upstage a September report on military and economic progress in Iraq.

Iraq’s political crisis also worsened as five more ministers announced a boycott of Cabinet meetings – leaving Prime Minister al-Maliki’s unity government with no members affiliated with Sunni political factions.

Mr. al-Maliki, meanwhile, arrived in Turkey for a state visit likely to be dominated by Turkish warnings to either crack down on rebel bases in northern Iraq or face a possible incursion. He was slated to travel to Iran on Wednesday.

The American military said three Task Force Marne soldiers were killed Saturday when a roadside bomb struck their convoy south of Baghdad, the military said.

One Multi-National Division – Baghdad soldier was killed and another wounded Monday when their vehicle was targeted by an armor-piercing explosively formed penetrator, or EFP, in a western section of the capital, according to a separate statement.

Washington has accused Iran of supplying Shiite extremists with EFPs to step up attacks against American forces. Tehran denies the allegations.

The military also said earlier that four soldiers were killed in a powerful combat explosion in restive Diyala province north of the capital on Monday.

The deaths raised to at least 19 members of the American military who have died this month, or a rate of about three per day, putting August on track for a heavier toll after a drop in July. Seventy-nine American troop deaths were reported, the lowest number since 70 killed in November.

More than 100 American forces died each month in the April-to-June period as the incoming American troops were deployed with the Iraqi army in Baghdad’s dangerous streets and security outposts.

Despite the relatively low number in July, Lieutenant General Raymond Odierno, the American second-in-command, has blamed nearly three-quarters of the attacks on rogue Shiite militias the military believes are being armed and trained by Iran, which he said was increasing its support ahead of the pivotal report to be delivered to Congress in September.

Despite the new American accusations of Iranian meddling, the American and Iranian ambassadors met Monday for their third round of talks in just over two months. The American Embassy called the talks between Ambassador Ryan Crocker and his counterpart, Hassan Kazemi Qomi, “frank and serious.”

The new cracks in Mr. al-Maliki’s government appeared even as American military officials sounded cautious notes of progress on security, citing strides against insurgents linked to Al Qaeda in Iraq but also new threats from Iranian-backed Shiite militias.

But it was Mr. 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 who 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 Mr. al-Maliki.

The Mr. 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.

“This decision is a bid to apply political pressure for reforming the political process that is headed in the wrong direction,” bloc spokesman Ayad Jamaluddin said Tuesday at a news conference.

He declined to give a deadline but said the bloc’s demands included reconsidering efforts to revise legislation to bring thousands of former Saddam Hussein era party officials back into the government and preventing the infiltration of security forces by extremists.

The ministers intend to continue overseeing their ministries.

Iraqi President 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 America 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,” Mr. 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 Mr. Allawi, said the boycott began with Monday’s Cabinet meeting.

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

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

Houses collapsed as many families were getting ready for the day ahead.

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.

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Associated Press writers Sinan Salaheddin and Hamid Ahmed in Baghdad contributed to this report.