BAGHDAD (AP) - Radical Shiite cleric Muqtada al-Sadr appeared in public for the first time in months on Friday, delivering a fiery anti-American sermon to thousands of followers and demanding U.S. troops leave Iraq.

It was not immediately clear why he chose to return now from Iran to his base in the Shiite holy city of Najaf. His speech had new nationalist overtones, calling on Sunnis to join with him in the fight against the U.S. presence. He also criticized the government's inability to provide reliable services to its people.

Al-Sadr's reappearance, four months after he went underground at the start of the U.S.-led Baghdad security crackdown, came as his Mahdi Army lost its commander in the southern city of Basra in a gunbattle with British soldiers, Iraqi police said.

The 33-year-old al-Sadr is believed to be honing plans to consolidate political gains and foster ties with Iran - and possibly trying to take advantage of the absence of a major rival, Supreme Islamic Council of Iraq leader Abdul-Aziz al-Hakim, who was recently diagnosed with lung cancer and went to Iran for treatment.

The U.S. military also announced Friday that six U.S. soldiers were killed in a series of attacks across Iraq in recent days. The deaths put May on pace to be one of the deadliest months for U.S. forces here in years.

Al-Sadr traveled in a long motorcade from Najaf to the adjacent holy city of Kufa on Friday morning to deliver his sermon before 6,000 worshippers.

"No, no for Satan. No, no for America. No, no for the occupation. No, no for Israel," he chanted in a call and response with the audience at the start of his speech.

He repeated his long-standing call for U.S. forces to leave Iraq.

"We demand the withdrawal of the occupation forces, or the creation of a timetable for such a withdrawal," he said. "I call upon the Iraqi government not to extend the occupation even for a single day."

He also condemned fighting between his Mahdi Army militia and Iraqi security forces, saying it "served the interests of the occupiers." Instead, he said the militia should turn to peaceful protests, such as demonstrations and sit-ins, he said.

Al-Sadr's Mahdi Army fought U.S. troops to a virtual standstill in 2004, but to avoid renewed confrontation he ordered his militants off the streets when the U.S. began its security crackdown in the Baghdad area 14 weeks.

Al-Sadr's associates say his strategy is based partly on a belief that Washington will soon start reducing troop strength, leaving a void in Iraq's security and political power structure that he can fill.

Al-Sadr also believes that Shiite Prime Minister Nouri al-Maliki's government may soon collapse under its failure to improve security, services and the economy, al-Sadr's aides say. A political reshuffle would give the Sadrist movement, with its 30 seats in the 275-member parliament, an opportunity to become a major player.

In a move that could hasten the collapse, al-Sadr pulled his supporters out of al-Maliki's government last month over the prime minister's refusal to call for a timetable for a U.S. withdrawal.

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 the volatile Diyala province, the military said.

The killings raised the American death toll for the month to at least 88. Last month, 104 U.S. troops were killed in Iraq.

Military officials have warned that U.S. casualties were likely to rise as 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."

Iraqi troops and soldiers have also been targeted by insurgents here, who accuse them of collaborating with U.S. forces.

Gunmen in a speeding car shot and killed a police officer as he was leaving his house in the Shiite-dominated al-Wihda district, 20 miles south of Baghdad on Friday morning, police said.

In al-Wijaihiya, about 60 miles northeast of Baghdad, a gunbattle between residents of a Sunni village and their rivals in a neighboring Shiite village, killing two people and injuring five others, police said. Seven hours of fighting ended only when the Iraqi army intervened.

The residents of al-Aswad, the Shiite village, accused the Sunnis from al-Khurair of harboring Sunni extremists who want to expel the Shiites. The Sunnis said the Shiites attacked them with mortar rounds.

In other violence, six mortar rounds hit houses in western Baghdad, killing one person, and a roadside bomb exploded at the entrance to a bridge in western Baghdad, damaging the span, police said. The blast was the latest attack on Baghdad's bridges by insurgents.