Influential Shi'ite cleric Moqtada al-Sadr said he rejects the Iraqi constitution backed by his partners in the biggest parliamentary bloc, threatening to reignite one of the country's most explosive issues."I reject this constitution which calls for sectarianism and there is nothing good in this constitution at all," he told Al Jazeera television late on Saturday.
Sadr, a rebel leader turned political kingmaker, said the charter was unacceptable, complicating efforts to form a government more than two months after parliamentary elections.
"If there is a democratic government in Iraq, nobody has the right to call for the establishment of federalism anywhere in Iraq whether it is the south, north, middle or any other part of Iraq," said Sadr.
His stand could give political ammunition to Iraq's Arab Sunnis, who want major amendments to a charter they fear will give Shi'ites and Kurds too much power and control over oil resources.
The young cleric, who led two armed uprisings against U.S. and Iraqi troops, has emerged as a potent force in Iraqi politics, joining the powerful United Iraqi Alliance (UIA), which won 128 of 275 seats in parliament in December 15 polls.
A swing vote by Sadr's supporters in a UIA ballot on its candidate for prime minister is likely to keep the Dawa party's Ibrahim al-Jaafari in the top job in government.
The Shi'ites, who will have a majority in the new assembly, have already insisted there can be no major changes to the charter, which was approved in October and envisages a federal Iraq with considerable autonomy for the regions.
Iraq's biggest Sunni political bloc has said it is committed to talks with Shi'ites and Kurds to form a government of national unity if its key demand on changing the constitution is met.
A review of the Iraqi constitution is set to start some time after the new government and parliament is formed.
Sadr's rejection of the charter could put him at the heart of one of the most sensitive sectarian issues in Iraq, where he is seen as an unpredictable but popular leader.
Sadr rose to prominence after the U.S.-led invasion of Iraq in 2003 by mobilizing his Mehdi Army militia to fight American troops and by speaking out for poor Shi'ites.
His uprisings against U.S. troops made him one of the few Shi'ite leaders to gain the respect of minority Sunnis, who dominated Iraq under Saddam Hussein and have led the insurgency against U.S. troops and the new Iraqi government.
Although Sadr has said his Mehdi Army was always ready to fight, he has maneuvered through political minefields to a position where he can make or break Iraqi leaders.
The young cleric recently went on a tour of Arab states, projecting a new image of a religious statesman. But Sadr always likes to remind people that his militia stands ready to fight.
"The Mehdi Army will serve the Arab and Muslim countries and will defend them whether in Syria or Iran," he told Al Jazeera.