Radical Shiite cleric Moqtada al-Sadr's political movement formally declared its withdrawal from Iraq's beleaguered ruling coalition on Monday at a Baghdad news conference.
Lawmaker Nassar al-Rubaie, flanked by allies from Sadr's 32-strong parliamentary bloc, said the group was pulling out of Prime Minister Nuri al-Maliki's unity government to push its demands for a withdrawal of US troops.
Rubaie read a statement which he said had been issued by Sadr, who has not himself appeared publicly since last year.
"Considering the public interest, we found that it was necessary to issue an order to the ministers of the Sadr bloc to immediately withdraw from the Iraqi government," the statement said.
"The six ministries shall be handed over to the government itself, hoping that this government would give these responsibilities to independent bodies who wish to serve the interests of the people and the country."
Rubaie said the group had come to the decision after Maliki ignored the demands of Shiite protesters who demonstrated last week in support of Sadr and demanded a timetable for US troop withdrawal.
"The main reasons are the prime minister's lack of response to the demands of nearly one million people in Najaf asking for the withdrawal of US forces and the deterioration in security and services," Rubaie told reporters.
On April 9, a rally organised by the group saw huge crowds of Shiites gather in the holy city of Najaf to demand the withdrawal of foreign troops from the war-ravaged country.
Estimates of the total size of the demonstration varied widely, with the US military reporting that 15,000 turned up while Iraqi officials claimed hundreds of thousands took to the streets.
Maliki has steadfastly refused to offer any timetable for withdrawal of foreign troops from Iraq, saying any decision on the departure of US-led forces will be guided by the security situation on the ground.