A secular bloc which won the most seats in Iraq's March 2010 vote suspended its participation in parliament on Saturday, sparking a political crisis just days after US forces ended their mission.
The Iraqiya bloc, led by ex-premier Iyad Allawi, walked out of parliament in protest at what it charged was Prime Minister Nuri al-Maliki's monopolising of decision-making.
The boycott represents one of Iraq's most serious political crises, and comes just a day after US forces handed over control of their last remaining base, with virtually all remaining American troops due out of the country in the coming days.
Iraqiya, which garnered most of its support from Iraq's minority Sunni community, was out-manoeuvred for the premiership by Maliki, who despite finishing second in the elections formed a larger coalition in their aftermath.
The bloc, which controls nine ministerial posts, has not, however, pulled out of Iraq's national unity government.
"We can no longer remain silent about the way the state is being administered, as it is plunging the country into the unknown," the bloc, which holds 82 seats in the 325-member legislature, said in a statement on Saturday.
"The Iraqiya bloc is suspending its participation in parliament from Saturday and calling for the opening of a round-table to find a solution that will support democracy and civil institutions."
It continued: "Iraqiya rejects this system of policy-making that consists of ignoring other political parties, politicising the justice system, exercising sole power and violating the law."
The bloc accused Maliki's government of "placing tanks and armoured cars in front of the homes of Iraqiya leaders in the Green Zone," the heavily-fortified home to leading politicians and ministers, as well as the US and British embassies, in central Baghdad.
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"This sort of behaviour drives people to want to rid themselves of the strong arm of central power as far as the constitution allows them to," it said, referring to moves by majority Sunni Arab provinces to take up the option of similar autonomy to that enjoyed by the Kurds in northern Iraq.
Votes in favour of autonomy by provincial authorities in Anbar, Salaheddin and Diyala have drawn an angry response from Maliki.
When the Salaheddin provincial council voted in October to push for autonomy, Maliki retorted that it "does not have the right to announce this," citing constitutional procedures that were not followed.
Ibrahim al-Jaafari, another ex-premier and head of Maliki's pan-Shiite National Alliance bloc, criticised Iraqiya's walkout and accused unspecified Sunni parties of using federalism, which they were hostile to when the constitution was approved in 2005, "to divide the country into regions".
"We are getting bogged down in a marginal fight instead of preparing ourselves for the withdrawal of foreign forces," Jaafari said in parliament.
The bloc loyal to anti-US cleric Moqtada al-Sadr offered to undertake a mediating role to resolve the dispute.
"Taking that sort of decision a day after the end of the US occupation is going to light the fire of division and we will do all can to put it out," Baha al-Araji, the leader of the movement's parliamentary bloc, said in a statement.
An independent lawmaker from the autonomous Kurdish region, Mahmud Othman, urged Maliki "to negotiate with all political parties so that Iraqiya does not feel marginalised."
But he also criticised Deputy Prime Minister Saleh al-Mutlaq, an Iraqiya member, for his rhetoric in a recent television interview, when he compared Maliki to a dictator worse than Saddam Hussein.
"This is not the way to speak of the head of government," Othman said.