Iraqi Forces, Al-Sadr's Militiamen Clash in Baghdad's Sadr City District

Iraqi government forces and Shiite militia fighters clashed anew Tuesday despite a government ultimatum to anti-American cleric Muqtada al-Sadr to either disband his Mahdi Army or give up politics.

Meanwhile, security forces were reported to be blocking al-Sadr's supporters from traveling to Baghdad from outlying areas to attend an anti-U.S. rally scheduled for Wednesday.

Al-Sadr called for the protest to mark the fifth anniversary of the capture of Baghdad by U.S. troops nearly a month after the war started, but many observers see it as a show of force in his confrontation with the government.

The fighting comes as Gen. David Petraeus, the commander of U.S. forces in Iraq, prepared to testify later Tuesday on the war.

He was expected to tell two Senate committees that last year's influx of 30,000 troops to Iraq had helped calm some of the sectarian violence but that to prevent a backslide in security, troops would likely be needed in large numbers through the end of the year.

A U.S. soldier died Tuesday from wounds received in a roadside explosion the night before in northeast Baghdad, raising to 11 the number of American troop deaths since Sunday.

In Baghdad, al-Sadr's organization was preparing to stage a "million-strong" anti-U.S. demonstration to mark the ouster of Saddam Hussein's regime from the capital.

But Sadrist officials in the provinces said Tuesday that security forces were preventing his followers from heading to the capital. They said supporters were being turned back at roadblocks near the towns of Kut, Najaf, Hillah and other locations.

The rapid tumble back to street battles in Baghdad — at an intensity not seen since last year's flood of U.S. troops into the city — is a worrisome backdrop to the planned appearance before Congress by Petraeus and Ambassador Ryan Crocker to report on progress in Iraq.

Hundreds of civilians have already fled Sadr City, where gunbattles have raged since last week. The sprawling district of some 2.5 million people, the nerve center of al-Sadr's Mahdi Army, has been under siege by about 1,000 U.S. and Iraqi troops.

Fighting broke out again early Tuesday after Iraqi units tried to enter the area, a police officer said.

The boom of explosions could be heard across the capital, apparently coming from the neighborhood in eastern Baghdad. Low-flying jets circled the center of the capital several hours before sunrise.

The two sides were using small arms, rocket-propelled grenades and mortars in the ongoing combat, said the police officer, who spoke on condition of anonymity because he was not authorized to release the information to the media.

Fifteen civilians have been injured in the clashes, he said.

Al-Sadr's aides said Monday that he would only dismantle the powerful militia — estimated at up to 60,000 — if ordered by top Shiite clerics, who have remained silent throughout the increasingly dangerous showdown.

With the crisis showing no sign of abating, Prime Minister Nouri al-Maliki raised the stakes on Sunday, telling CNN that al-Sadr and his followers would not be allowed to participate in politics or run in provincial elections this fall "unless they end the Mahdi Army."

Al-Maliki's statement followed a weekend declaration by top Shiite, Sunni and Kurdish leaders to support legislation banning any party that maintained a militia.

An al-Sadr aide, Hassan al-Zarqani, told The Associated Press by telephone from Iran that the Sadrists would consult Grand Ayatollah Ali al-Sistani and other top Shiite clerics in Iraq. If they "recommend he disband the Mahdi Army, he will obey," al-Zarqani said.

The crisis erupted March 25 when al-Maliki launched a crackdown against Shiite militias and so-called "criminal gangs" in the southern port city of Basra.

Elsewhere, unidentified gunmen early Tuesday attacked the home of a Sunni tribal leader working with the U.S.-sponsored Awakening Council, killing him and his three sons, Iraqi police said.

Police said the man, whose name was not given, was active in the Awakening Council in the Sunni-dominated area around the town of Baqouba, 50 miles north of Baghdad. U.S.-allied Sunni fighters, who have turned against Al Qaeda in Iraq, have been frequently targeted since they helped reduce violence in their areas.

Also, Iraqi police said a roadside bomb struck a minibus northeast of Baghdad, killing at least six civilians and wounding 10 others. The blast struck morning commuters in the Dahalkah area on the outskirts of the religiously mixed city of Balad Ruz.

In Tehran, Iran's foreign ministry for the first time condemned the repeated shelling of Baghdad's Green Zone in the past several days by al-Sadr's militiamen. Two U.S. soldiers died in there on Sunday.

But spokesman Mohammad Ali Hosseini also denounced attacks by Iraqi and American forces in Sadr City, calling on all sides to show restraint.