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

The U.S. military also announced 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 had gone into hiding in Iran four months ago at the start of the U.S.-led Baghdad security crackdown. It was not immediately clear why he chose to return now to his base in the Shiite holy city of Najaf.

However, he could be 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.

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.

As part of his effort to recast himself as a nationalist — instead of a radical with a narrow Shiite agenda — the 33-year-old leader called on Sunnis to join with him in the fight against the U.S. troop presence here. He also criticized the government's inability to provide reliable services to the people.

Al-Sadr is believed to be honing plans to consolidate political gains and foster ties with Iran.

His 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.

His associates say his strategy is based partly on a belief that Washington soon will start reducing troop strength, leaving behind a hole 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.