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Prime Minister Nouri al-Maliki's government faced a threat Tuesday by the main Sunni bloc in parliament to withdraw its Cabinet members if he doesn't meet a series of demands in the next 48 hours.

The Iraq Accordance Front, which has six Cabinet members and 44 of parliament's 275 seats, called for a pardon for security detainees not charged with specific crimes and the disbanding of militias, among other demands. But the government said the move amounted to blackmail and said the Sunni bloc had contributed in creating some of the very policies it now criticized.

A Sunni insurgent group jumped into the debate with an Internet statement posted Tuesday that called on the Accordance Front to follow through on its threat.

"We repeat our call to the Accordance Front to withdraw from the government and from the political process that gave those who elected it more killing, displacement and misery," the Islamic Army in Iraq said.

Separately, officials said the Kurdish chief of staff of Iraq's armed forces, Gen. Babaker B. Shawkat Zebari, had tendered his resignation to al-Maliki on Sunday but it was rejected by the Iraqi leader.

Prominent Kurdish lawmaker Mahmoud Othman said Zebari had been frustrated by what he believed was excessive interference by the Shiite prime minister and the Sunni Arab defense minister.

Zebari could not be reached for comment and it was not immediately clear whether he had agreed to stay on. His action, however, adds to the troubles of the embattled al-Maliki, who also holds the position of armed forces' commander in chief.

The U.S. military said Tuesday that a Marine was killed in fighting west of the capital, pushing the American death toll for July to at least 73, the lowest in eight months.

An Apache helicopter also went down Tuesday after coming under fire in a predominantly Shiite area in eastern Baghdad, but both crew members were safely evacuated, the military said.

U.S. military spokesman Lt. Col. Christopher Garver said it was not known if the AH-64 had been damaged in the precautionary landing. The incident was under investigation.

U.S. President George W. Bush's nominee to head the Joint Chiefs of Staff, meanwhile, acknowledged that slow progress in Iraq is hurting America's credibility and emboldening Iran's regional ambitions.

While steady progress has been made on the military front, Iraq's political factions have made only limited headway in achieving reconciliation, said Navy Adm. Michael Mullen, who has been nominated to replace U.S. Gen. Peter Pace as the nation's top military officer.

Iraq's parliament shrugged off U.S. criticism and adjourned for a month, as key lawmakers declared there was no point waiting any longer for Prime Minister al-Maliki to deliver Washington-demanded benchmark legislation for their vote.

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

The recess, coupled with 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.

The U.S. military said the Marine was killed Monday while conducting combat operations in the vast Anbar province west of Baghdad.

The attack raised to at least 73 the number of U.S. service members who have died in Iraq in July, the lowest number since November 2006, when at least 70 U.S. deaths were reported. The monthly toll topped 100 in April, May and June.

In all, at least 3,652 members of the U.S. military have died since the Iraq war started in March 2003, according to an Associated Press count. The figure includes seven military civilians. At least 2,997 died as a result of hostile action, according to the military's numbers.

The No. 2 commander in Iraq, Lt. Gen. Ray Odierno, expressed cautious optimism about the downturn last week. He said it appeared that casualties had increased as U.S. forces expanded operations into militant strongholds as part of a more than five-month-old security crackdown aimed at clamping off violence in the capital, but were going down as the Americans gained control of the areas.

"We've started to see a slow but gradual reduction in casualties, and it continues in July," he said Thursday at a news conference. "It's an initial positive sign, but I would argue we need a bit more time to make an assessment whether it's a true trend."

An unmanned U.S. drone also crashed late Monday while landing at an air base north of Baghdad, but it did not appear to be from hostile activity and no casualties were reported, the military said separately.

The U.S. has an estimated two dozen or more unmanned MQ-1 Predators doing surveillance over Iraq. They have become mainstays of the U.S. war effort, offering round-the-clock airborne "eyes" watching over road convoys, tracking nighttime insurgent movements via infrared sensors, and occasionally unleashing one of their two Hellfire missiles on a target.

In scattered violence reported by police on Tuesday, at least 11 people were killed or found dead nationwide, including three Iraqi police in a drive-by shooting and one soldier in a roadside bombing. A teacher also was shot to death while driving to work in a mainly Sunni neighborhood in a western part of the capital.

Complete coverage is available in FOXNews.com's Iraq Center.