BAGHDAD - Iraq's parliament on Monday shrugged off U.S. criticism and adjourned for a month, as key lawmakers declared there was no point waiting any longer for the prime minister to deliver Washington-demanded benchmark legislation for their vote.

Speaker Mahmoud al-Mashhadani closed the final three-hour session without a quorum present and declared lawmakers would not reconvene until Sept. 4. That date is just 11 days before the top U.S. military and political officials in Iraq must report to Congress on American progress in taming violence and organizing conditions for sectarian reconciliation.

The recess, coupled with Prime Minister Nouri al-Maliki's failure to get the key draft laws before legislators, may nourish growing opposition to the war among U.S. lawmakers, who could refuse to fund it.

Critics have questioned how Iraqi legislators could take a summer break while U.S. forces are fighting and dying to create conditions under which important laws could be passed in the service of ending sectarian political divisions and bloodshed.

But in leaving parliament, many lawmakers blamed al-Maliki.

"Even if we sit next month, there's no guarantee that important business will be done," said Mahmoud Othman, a prominent Kurdish legislator. The parliament had already extended its session by a month, having initially planned a recess for July and August.

"There are Iraqi-Iraqi and Iraqi-American differences that have not been resolved," Othman said of the benchmark legislation. "The government throws the ball in our court, but we say that it is in the government's court and that of the politicians. They sent us nothing (to debate or vote)."

The September reports by Ambassador Ryan Crocker and U.S. commander Gen. David Petraeus were to assess progress by the Iraqi government and its security forces on 18 political and security benchmarks.

Those include a so-called oil law that would set out rules for foreign investment and the fair distribution of revenue to all of Iraq's sects and ethnic groups.

"We gave the government a good chance by continuing to sit in July. We can still return for an emergency session if that's required, but I don't think that this is necessary because the draft legislation is not complete," said Salem Abdullah, spokesman for the Iraqi Accordance Front, the key Sunni bloc in parliament.

In Washington, the State Department was unusually silent on the matter, declining to criticize the lawmakers for the break.

"There's a lot of work to be done in Iraq," deputy spokesman Tom Casey said. "I'll leave it to the parliamentary leaders themselves to explain why this might be a good time to take a break."

He said the United States would continue to push for work on critical legislation, including pieces like the oil law, during the vacation.

"Whether the parliament is in session or not, I think we expect that all of Iraq's political leadership is going to be continuing to work on those kinds of issues and work out the kinds of compromises so that when the parliament does come back into session, there'll be something there for them to vote on and them to act on," Casey said.

"This is not just about having the votes," he said. "It's about doing the work in advance so that there's actually legislation there that folks can agree on."

Meanwhile, al-Maliki faces a revolt within his party by factions that want him out as Iraqi leader, according to officials in his office and the political party he leads.

Ibrahim al-Jaafari, al-Maliki's predecessor, leads the challenge and already has approached leaders of the country's two main Kurdish parties, parliament's two Sunni Arab blocs and lawmakers loyal to powerful Shiite cleric Muqtada al-Sadr.

Al-Jaafari's campaign, the officials said, was based on his concerns that al-Maliki's policies had led Iraq into turmoil because the prime minister was doing too little to promote national reconciliation.

The former prime minister also has approached Grand Ayatollah Ali al-Sistani, Iraq's top Shiite cleric, proposing a "national salvation" government to replace the al-Maliki coalition. The Iranian-born al-Sistani refused to endorse the proposal, the officials said.

"Al-Jaafari is proposing a national and nonsectarian political plan to save the nation," Faleh al-Fayadh, a Dawa party lawmaker familiar with the former prime minister's contacts.

Other officials, however, said al-Jaafari had only an outside chance of replacing or ousting al-Maliki. But they said the challenge could undermine al-Maliki and further entangle efforts at meeting important legislative benchmarks sought by Washington.

All the officials spoke of the sensitive political wrangling only on condition of anonymity.

Also Monday, a small bus exploded in a central Baghdad market district, killing at least six people -- a brutal reminder of the dangers facing Iraqis who celebrated in the streets by the tens of thousands Sunday night after their national team won the prestigious Asian Cup soccer tournament.

Black smoke rose into the air after the blast struck a transit point near Tayaran Square, damaging several nearby cars and kiosks selling clothes, fruit and juice, police and hospital officials said. The minibus was one of several waiting for passengers heading to predominantly Shiite areas in eastern Baghdad.

At least 31 people were wounded, according to the officials, who spoke on condition of anonymity because they weren't authorized to release the information.

A total of 42 Iraqis were killed or found dead nationwide, according to police, hospital and morgue officials.

The U.S. military said three soldiers were killed in fighting in Anbar province west of Baghdad on Thursday. At least 3,651 members of the U.S. military have died since the start of the Iraq war in March 2003, according to an Associated Press count.