BAGHDAD: The secular Iraqiya bloc, which won most of the votes of Iraq's disenchanted Sunni Arab minority, walked out of parliament on Saturday sparking a political crisis days after US forces ended their mission.

The bloc, led by former premier Iyad Allawi, said it was suspending its participation in parliamentary business in protest at what it charged was Prime Minister Nuri al-Maliki's monopolisation of all decision-making.

"We can no longer remain silent about the way the state is being administered, as it is plunging the country into the unknown," said the bloc, which holds 82 of the 325 seats in parliament, second only to Maliki's National Alliance.

"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 said.

"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 the Maliki government of "placing tanks and armoured cars in front of the homes of Iraqiya leaders in the Green Zone," the heavily fortified central Baghdad district that houses the official residences of leading politicians and government ministers as well as the British and U.S. embassies.

"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 in allusion 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 the provincial authorities in Anbar, Salaheddin and Diyala have drawn an angry response from the prime minister.

When Salaheddin provincial council voted in October to push for autonomy, Maliki retorted that it "does not have the right to announce this."

"Federalism is a constitutional issue," he said, insisting that the provincial council should have presented a request to the cabinet, which would then present it to parliament.

Article 119 of the Iraqi constitution states: "One or more governorates shall have the right to organise into a region based on a request to be voted on in a referendum submitted in one of the following two methods."

These are: "A request by one-third of the council members of each governorate intending to form a region," or "a request by one-tenth of the voters in each of the governorates intending to form a region."

The walkout by Iraqiya MPs represents one of Iraq's most serious political crises and comes a day after US forces handed over control of their last remaining base.

The Shiite radical movement of firebrand cleric Moqtada al-Sadr said it was ready to undertake a "mediation mission to try to secure a change of heart".

"Taking that sort of decision a day after the end of the U.S. occupation is going to light the fire of division and we will do all can to put it out," the the leader of the movement's parliamentary bloc Baha al-Araji.