In an attack in western Baghdad, 50 people were killed and 60 wounded when a suicide attacker exploded a fuel truck near a gas station. Another car bomb attack in central Baghdad left 17 dead, reported the Associated Press.
Meanwhile, the U.S. military announced the death of four American soldiers, including three from an armor-piercing bomb. Britain also said one of its soldiers died in a roadside bombing in Basra, according to the AP.
Rafaa al-Issawi, a leading member of the Sunni Accordance Front, said at a news conference that the six Cabinet ministers were resigning because of Shiite Prime Minister Nouri al-Maliki's failure to meet certain demands, including a larger role for the Front in security matters.
"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.
The Front had given al-Maliki seven days to meet its demands, and Wednesday was the deadline.
Along with more involvement in security matters, the Front's demands included a pardon for security detainees not charged with specific crimes and the disbanding of militias.
The Front's 44 members will remain in the 275-seat parliament. Their departure would have little effect on the government, which is almost paralyzed by infighting but needs a simple majority to continue functioning, according to Reuters.
Iraq Vice President Tareq al-Hashemi, a Sunni, said the Front was still open to negotiating.
"The doors are still open on all options, including returning to government, if they introduce reforms," he said, Reuters reported.