Ammar al-Hakim, who is being groomed to take over the Supreme Islamic Iraqi Council, the country's largest Shiite party, has been a firm supporter of federalism from the outset.
But his unusually strident language appeared to signal growing impatience with Prime Minister Nouri al-Maliki's inaction on key issues and his failure to bring fractured groups together.
Addressing hundreds of supporters at the party's Baghdad headquarters, al-Hakim called on Iraqis to press ahead with the creation of self-rule regions, but cautioned that the country's unity must be safeguarded.
"Federalism is one way to accomplish this goal,'' he said.
He said Baghdad's monopoly of power over decision-making and national wealth had turned the central government into a "tyrannical and dominating'' body.
"I call on the sons of our nation to create their (self-rule) regions,'' al-Hakim said.
The idea of breaking up Iraq into self-rule entities has gained traction in Washington after two legislators _ Senator Joseph Biden (D-Del.) and Senator Sam Brownback (R-Kan). _ proposed giving more control to ethnically and religiously divided regions.
A non-binding resolution to that effect won Senate approval last month, but Republicans supported it only after the measure was amended to make clear that President George W. Bush should press for a new federalized system only if the Iraqis wanted it.
Al-Maliki and other Iraqi politicians denounced the decision as an infringement on Iraq's sovereignty. But President Jalal Talabani, a Kurd and firm proponent of federalism, praised the resolution, saying it cemented Iraq's unity and opposed its breakup.
Al-Hakim is the son of Abdul-Aziz al-Hakim, the Supreme Council leader who was diagnosed with cancer in May and has been receiving chemotherapy treatment in Iran.
The younger al-Hakim delivered the remarks in a sermon commemorating the start of the Muslim Eid al-Fitr feast that marks the end of Ramadan, the Islamic month of fasting. His father, the organization's patriarch, greeted well-wishers at the ceremony but did not address the crowd.
The Supreme Council has been a staunch backer of federalism and wants the country's mainly Shiite and oil-rich south to become a self-rule region similar to that established 16 years ago by minority Kurds in northern Iraq.
The Iraqi constitution, adopted two years ago, provides for a federal system. A year ago, parliament pushed through a law allowing the formation of federal regions but not for 18 months.
Regardless, federal regions cannot be formed before national elections are held for local councils. Those councils will decide on seeking union with other provinces to form a federal region. No date has been set for the vote because parliament has yet to pass legislation on the organization of local elections.
The law is one of several Washington has been pressing al-Maliki's government to push through parliament to enhance reconciliation. Others would ensure equitable distribution of oil wealth and reinstatement of Saddam Hussein loyalists in government jobs.
Al-Maliki has failed to achieve progress on the wanted legislation despite a major eight-month-old security drive in Baghdad and surrounding regions that was launched in part to give him the room he needs to make political compromises.
The joint U.S.-Iraqi operation has reduced the level of violence but failed to stem it altogether. On Saturday, a spokesman said Iraqi forces clashed with suspected al-Qaida-linked insurgents during a four-day operation in a Sunni enclave in central Baghdad.
Brig.-Gen. Qassim al-Moussawi, an Iraqi military spokesman, said 48 gunmen were killed in the fighting, in which Iraqi army soldiers were supported by local Sunni tribesmen and other civilians who have turned against al-Qaida in the volatile Fadhil neighbourhood.
Security is the main concern in Iraq, more than four years after the U.S. invasion, but the question of federalism is potentially explosive and could deepen the sectarian divide.
Iraq's once-dominant Sunni Arabs, for example, fear that it would lead to the country's breakup into a Shiite south and a Kurdish north, both with considerable oil wealth, leaving Sunnis the resource-poor central region. They see the creation of an autonomous region in the south as a scheme engineered by Shiite, non-Arab Iran to gain a permanent foothold in Iraq.
But not all of Iraq's majority Shiites back autonomy.
The Sadrists, a parliamentary bloc loyal to anti-American Shiite cleric Muqtada al-Sadr, are strongly opposed to it, while others, like al-Maliki's Dawa party, warn that federalism could deepen Iraq's security and sectarian woes if implemented soon.
