BAGHDAD (AP) - 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 later in the day.

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 stand 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.

Also, a fuel tanker exploded near a gas station in western Baghdad's primarily Sunni Mansour neighborhood, killing at least 50 people and wounding 60, police said. Two police officers, both speaking on condition of anonymity out of security concerns, said it was the work of a suicide attacker.

Earlier, a parked car bomb killed 17 civilians and left a gaping crater in a busy square in central Baghdad, police said. Another 32 people were wounded by the blast, another police officer said on the same condition of anonymity.

An Associated Press reporter at the scene said the explosion ripped a hole five feet wide in the asphalt. Three minibuses and six cars were damaged by flames and flying debris. Blood pooled in the street.

A gas station and a popular ice cream parlor also suffered damage. Windows were shattered and benches lay toppled outside. Shrapnel scattered 200 meters from the blast.

The explosives had been in a vehicle in al-Hurriyah square in the mostly Shiite Karradah neighborhood, and detonated around 10:15 a.m., the police officer said.

The bombing occurred nearly a week after a cluster of explosions, including one from a massive truck bomb, hit the same neighborhood. Karradah had previously been thought to be one of central Baghdad's safest areas. Last Thursday's blasts killed more than 60 people.