Four U.S. soldiers have been killed by roadside bombs in the Baghdad area, the military said Tuesday, raising to at least 19 the number of troop deaths in the first week of August.
The latest casualty figures could signal a resurgence in attacks after July's eight-month low.
Meanwhile, Iraq's political crisis worsened, with five more ministers boycotting Cabinet meetings - leaving Prime Minister Nouri al-Maliki's unity government without a Sunni political bloc.
The new cracks in al-Maliki's government appeared even as U.S. 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.
Three Task Force Marne soldiers were killed Saturday when a roadside bomb struck their convoy south of Baghdad, the military said.
One coalition soldier was killed and another wounded Monday when their vehicle was hit 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.
U.S. commanders have warned they expect militants to try to upstage a September report on military and economic progress in Iraq.
The deaths raised to at least 19 members of the U.S. 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 U.S. troops were deployed with the Iraqi army in Baghdad's dangerous streets and security outposts.
Despite the relatively low number in July, Lt. Gen. Raymond Odierno, the U.S. 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.
The U.S. and Iranian ambassadors met Monday for their third round of talks in just over two months. The U.S. Embassy called the talks between 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 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 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.
From NPR reports and The Associated Press