Hours later, the notorious leader of al-Sadr's Mahdi Army militia in the city of Basra was killed in a shootout as British and Iraq troops tried to arrest him, police and the British military said, further enflaming tensions in the Shiite areas of southern Iraq.

The U.S. military also announced Friday the deaths of six U.S. soldiers, putting May on pace to be one of the deadliest months for U.S. forces here in years.

Al-Sadr went underground ¡ª reportedly in Iran ¡ª at the start of the U.S.-led security crackdown on Baghdad 14 weeks ago. He also had ordered his militia off the streets to prevent conflict with U.S. forces.

Radical Shiite cleric Muqtada al-Sadr delivers his sermon before 6,000 worshippers in holy Shiite city of Kufa 160 kilometers (100 miles) south of Baghdad, Iraq on Friday, May 25, 2007.[AP]

His return to the Shiite holy city of Najaf appeared to be an effort by the 33-year-old firebrand cleric to regain control over his militia, which had begun fragmenting, and to take advantage of the illness of a Shiite rival. There had also been some indication that his absence from the national arena was costing him political support.

Al-Sadr drove in a long motorcade from Najaf to its sister city of Kufa to deliver an anti-American sermon to 6,000 chanting supporters at the main mosque.

"No, no for Satan. No, no for America. No, no for the occupation. No, no for Israel," the glowering, black-turbaned cleric chanted in a call and response with the crowd.

"We demand the withdrawal of the occupation forces, or the creation of a timetable for such a withdrawal," he said, wiping sweat from his brow with a white cloth as temperatures hovered at 113 degrees. "I call upon the Iraqi government not to extend the occupation even for a single day."

While the call for a U.S. pullout was nothing new, al-Sadr also peppered his speech with nationalist overtones, criticizing the government for not providing services, appealing to his followers not to fight with Iraqi security forces and reaching out to Sunnis.

"To our Iraqi Sunni brothers, I say that the occupation sows dissension among us and that strength is unity and division is weakness," he said. "I'm ready to cooperate with them in all fields."

Al-Sadr did not address his reasons for returning.

However, during his time in absentia his militia appeared to have split into a faction calling itself the "noble Mahdi Army" and more extremist elements that it accuses of killing innocent Sunnis and embezzling funds. Some members of the more moderate faction were even willing to provide the U.S. military with information on their rivals in an effort to purge the militia.

In addition to trying to rein in the force, Al-Sadr is also believed to be honing plans to consolidate political gains and foster ties with Iran ¡ª and possibly trying to capitalize on the illness of Supreme Islamic Council of Iraq leader Abdul-Aziz al-Hakim, who was recently diagnosed with lung cancer and went to Iran for treatment.

Anthony Cordesman, an analyst at the Center for Strategic and International Studies, said al-Sadr might have come back to try to garner Sunni support, establish himself as a critic of Prime Minister Nouri al-Maliki and take the mantle as the leading Iraqi opponent of the U.S. presence here.

"In doing so, he can ride a wave of public opinion that sees the U.S. as having failed, coalition forces as a 'threat,' and is deeply frustrated with a weak Maliki government," he wrote in an analysis.

Al-Sadr's associates say his strategy rests in part on his belief that Washington will soon start reducing troop strength, leaving behind a hole in Iraq's security and political power structure that he can fill. He also believes al-Maliki's government may soon collapse because of its failure to improve security, services and the economy, they say.

In Washington, National Security Council spokesman Gordon Johndroe expressed hope that al-Sadr's reappearance signaled he wanted "to play a positive role inside Iraq."

"He has an opportunity to be a part of the political reconciliation process. We'll see if he and his followers participate," he said.

Later Friday, the Mahdi Army received a blow when its Basra leader, Wissam al-Waili, 23, also known as Abu Qadir, was shot and killed along with his brother and two aides during a gunbattle with British and Iraqi troops, police and the British military said.

The battle began about 4 p.m. during a raid to arrest al-Waili in Jumhoriyah, a middle class, residential area in central Basra, police said. Al-Waili and his three companions opened fire and were killed when the troops shot back, police said.

Several hours later, Mahdi Army militants broke into the home of a former top Iraqi officer in Basra, set one Humvee on fire and stole another.

Al-Sadr's return came amid signs that the sectarian violence which plagued Iraq last year was rising again, despite the U.S. crackdown.

U.S. military officials have said the number of bodies found blindfolded, shot and usually with signs of torture is an effective indicator of the intensity of the violence between Sunnis and Shiites. In February, when the crackdown began, the number was 640, down from 1,079 the month before, according to an Associated Press count. In the first 24 days of May, the number was 855, which would work out to more than 1,100 if the pace of killing continues at the current rate.

Meanwhile, three U.S. soldiers were killed in roadside bombings in the capital and the surrounding areas, the military said Friday. Two others were killed in explosions north of Baghdad, and a sixth soldier was hit by gunfire in Diyala province, the military said.

The killings raised the American death toll for the month to at least 88 through May 24. That average of nearly 3.7 deaths a day ¡ª if it continues ¡ª would work out to 113 deaths for the month, the most since 137 soldiers were killed in November 2004, when U.S. troops were fighting insurgents in Fallujah.

Military officials have warned that U.S. casualties were likely to rise because more troops deployed to Iraq and the military pushed ahead with its Baghdad security crackdown.

"As we are conducting more operations, we are going into areas we haven't gone into in force before. We have more people on the ground, this leads to an opportunity for more contact, more conflict, more clashes," said Lt. Col. Christopher Garver, a U.S. military spokesman. "This is a tough fight. We are in a war."