Iraqis mill around the site where a parked car bomb killed 17 civilians and wounded 12 today. Five cars were incinerated by the blast, which occurred in al-Hurriyah square in the Karradah neighborhood, where explosives had been planted in a vehicle.

BAGHDAD — Iraq's largest Sunni Arab political bloc announced its withdrawal from the government today, undermining efforts to seek reconciliation among the country's rival factions, and two bombing attacks in Baghdad killed at least 67 people.

In one attack, 50 people were killed and 60 wounded when a suicide attacker exploded a fuel truck near a gas station in western Baghdad. Another 17 died in a separate car bomb attack in central Baghdad.

The U.S. military announced the deaths of four American soldiers, three of whom were killed by a sophisticated, armor-piercing bomb. Britain also announced the death of one of its soldiers, by a roadside bomb in Basra.

Rafaa al-Issawi, a leading member of the Front, said at a news conference that the bloc's six Cabinet ministers would submit their resignations today.

Al-Issawi said the decision to pull out from the government followed what he called Prime Minister Nouri al-Maliki's failure to respond to the Accordance Front. It gave him seven days to meet its demands, and the ultimatum expired today.

Among the demands: a pardon for security detainees not charged with specific crimes, the disbanding of militias and the participation of all groups represented in the government in dealing with security issues.

"The government is continuing with its arrogance, refusing to change its stance and has slammed shut the door to any meaningful reforms necessary for saving Iraq," al-Issawi said.

"We had hoped that the government would respond to these demands or at least acknowledge the failure of its policies, which led Iraq to a level of misery it had not seen in modern history. But its stand did not surprise us at all," he said, reading from a prepared statement.

The Accordance Front has 44 of parliament's 275 seats. Its withdrawal from the 14-month-old government is the second such action by a faction of al-Maliki's "national unity" coalition.

Five Cabinet ministers loyal to radical Shiite cleric Muqtada al-Sadr quit the government in April to protest al-Maliki's reluctance to announce a timetable for the withdrawal of U.S. forces from Iraq.

The U.S. military today announced the deaths of three more soldiers, killed by a sophisticated, armor-piercing bomb in eastern Baghdad. An explosively-formed penetrator, or EFP, detonated near the soldiers' patrol during combat operations Tuesday, it said. Six other soldiers were wounded.

Another soldier was killed by small arms fire Tuesday in a separate incident, the military reported. All of the victims' names were withheld pending family notification.

That brought to 76 the July toll of U.S. deaths in Iraq. It was the lowest monthly count in eight months, as the U.S. military said it was gaining control of former militant strongholds.

Still, it was the deadliest July for U.S. troops since the war began. For the previous three years, the month of July saw a relatively low death toll. In July 2006, 43 U.S. troops were killed in Iraq, and 54 died in each of the previous two Julys.

By contrast, July was the second-deadliest month for Iraqis so far this year, according to an Associated Press tally.

In other violence today, Iraqi police said a parked car bomb killed three people and wounded five in southern Baghdad in a mostly Christian area.

The U.S. military said its forces had killed three suspects and captured 27 others in raids targeting al-Qaida in Iraq on Tuesday and today.