BAGHDAD -- A powerful anti-American Shiite cleric threatened Saturday to reactivate his feared militia if U.S. soldiers remain in Iraq beyond this year, following an offer by the Obama administration to keep troops on if they are needed.

Eight years to the day after former dictator Saddam Hussein was ousted, cleric Muqtada al-Sadr issued a statement to his followers that stopped just short of calling for violent action against U.S. forces. He accused "the occupation" of inciting panic, corruption and unrest among Iraqis.

His statement was read aloud at a huge protest of tens of thousands in Baghdad's Mawal Square, near al-Sadr's Sadr City stronghold. The cleric is in Iran, where he has been studying religion for the last several years.

"What if the invasion forces will not leave our lands?" al-Sadr said in the statement, which was read at the protest by his aide Salah al-Obeidi. "What if the U.S. forces and others stay in our beloved lands? What if their companies and embassy headquarters will continue to exist with the American flags hoisted on them? Will you be silent? Will you overlook this?"

"No, no America. No, no America," the crowd shouted in reply.

In January, al-Sadr visited his ancestral home in the holy Shiite city of Najaf, 100 miles south of Baghdad, and told followers to embrace a peaceful approach to diplomacy as his political wing gains power in Iraq's government. But he also said that should the U.S. troops remain in Iraq past 2011, followers might retaliate "by all means of resistance."

On Saturday, al-Sadr elaborated on that point explaining he would quickly train newly armed followers and bring his feared Mahdi Army militia out of retirement. "We will have to adopt (this) approach if they will not leave our country," he said.

The Mahdi Army ran rampant in Baghdad, Basra and other Iraqi cities at the peak of Iraq's violence a few years ago, raiding homes and killing Sunnis in the widespread sectarian fighting that brought the country to the brink of civil war. Al-Sadr froze the militia after it was roundly defeated by Iraqi forces in Basra in 2008, dramatically reducing violence in the country.

Under a security agreement between Washington and Baghdad, U.S. troops are scheduled to leave Iraq at the end of 2011. Prime Minister Nouri al-Maliki, who needed al-Sadr's support to keep his job after his party failed to win a majority in national elections last year, has said repeatedly he believes the American forces will no longer be needed in Iraq by next year.

But many Sunni and Kurdish lawmakers want U.S. troops to stay, fearing Iraq is still too unstable to be able to protect itself should Iran begin to play a more active role in the country after American forces leave.

Visiting Iraq this week, U.S. Defense Secretary Robert Gates said the Obama administration is willing to keep troops in Iraq past 2011. After meeting with al-Maliki and other leaders during his two-day visit, Gates signaled that scenario was becoming increasingly likely.

Haidar Nuaman, 25, one of the demonstrators, said al-Sadr's statement shows that many Iraqis won't stand for a continued U.S. military presence.

"It seems that the government does not know what to do. Muqtada's is an important voice to stand against any intention by the government to extend the presence of forces," he said.