BAGHDAD, Iraq — The Shiite heir apparent to a key U.S. political ally added his voice Saturday to calls for the division of Iraq into semi-autonomous regions based on sect and ethnicity, throwing down a gauntlet on an issue that has stirred fierce emotions in Iraq.

Ammar Hakim's appeal before hundreds of supporters gathered for prayers marking the end of the Muslim holy month of Ramadan came just weeks after passage of a nonbinding Senate resolution calling for a devolution of power to three self-governing regions for Shiites, Sunnis and Kurds.

Iraqi politicians responded angrily to the resolution, which was sponsored by Sen. Joseph R. Biden Jr., a Delaware Democrat who is a candidate for president. Iraqi Prime Minister Nouri al-Maliki, a Shiite, called the measure an infringement on Iraqi sovereignty. Others accused officials in Washington, D.C. , of plotting to partition Iraq.

But the idea of building strong regions has the support of Kurdish leaders, including President Jalal Talabani, and the Supreme Islamic Iraqi Council, one of the two largest Shiite formations, led by Hakim's father, Abdelaziz Hakim.

The Kurds have a self-governing state in the north, which they hope to expand by annexing the oil-rich city of Kirkuk and other disputed areas. Abdelaziz Hakim has called for uniting the nine provinces in the south with a Shiite majority into a similar region.

"I call on this holy day for the people of my country to form the (self-governing) regions, starting with the region south of Baghdad," Hakim's son said in a sermon delivered outside the party headquarters in Baghdad, the capital. "It is an Iraqi interest, wish and decision."

But he also stressed the need to preserve Iraqi unity and said federalism was the best way to achieve this.

The principle of federalism is enshrined in the Iraqi constitution, but politicians have yet to agree on a bill outlining the relationship between central and provincial authorities, one of the benchmarks for continued U.S. support.

Sunni political leaders are among the strongest opponents because they fear the largely barren western area where they dominate would be shut out from the oil wealth in the north and south.

Abdelaziz Hakim's main Shiite rival, anti-American cleric Muqtada al-Sadr, also advocates a strong central government. The two leaders signed a cease-fire Oct. 6 aimed at ending gunfights between their allied militias that had raised fears of a new front in the Iraq war.

Ammar Hakim has taken the helm of his party since his father was diagnosed with cancer in May. The elder Hakim attended Saturday's sermon, greeting well-wishers at his first public appearance since returning this week from Iran, where he went for treatment.

Abdelaziz Hakim has cultivated close ties with the United States and Iran, despite the rivalry between them. His son urged further talks between the two countries, whose envoys have met twice this year to discuss Iraq's security.

U.S. officials accuse Iran of arming and financing Shiite militants who have attacked their forces in Iraq. Officials in Tehran, the Iranian capital, deny the charges and charge that it is the continued U.S. presence that is fueling the violence in Iraq.

Ammar Hakim urged U.S. forces to exercise greater caution when targeting militants, pointing to recent bombings that have killed civilians. He also ruled out the idea of permanent U.S. bases.

The Bush administration denies it is seeking permanent bases in Iraq, but officials have spoken of keeping a reduced number of troops here for a prolonged period of time.

Violence was relatively muted Saturday, as Iraq's Shiite majority joined Sunnis in celebrating the end of the fasting month of Ramadan by visiting relatives and picnicking at a popular Baghdad park.

The U.S. military confirmed in a statement that two U.S. troops were killed in a mortar barrage on Camp Victory outside of Baghdad on Wednesday. The deaths were reported previously, but the military had not identified them as U.S. troops.

Police reported the deaths of at least 14 people in shootings and clashes in Babil, a province south of Baghdad where rival tribes and militias are competing for influence. Three more bodies were recovered in Baghdad, apparent victims of sectarian killings.