Followers of Shi'ite cleric Moqtada al-Sadr marched on Friday against a pact letting US forces stay in Iraq until 2011, toppling an effigy of President George Bush where US troops once tore down a statue of Saddam Hussein.
Thousands of demonstrators chanted and waved Iraqi flags in Baghdad's Firdos Square, protesting the security pact even though it includes a withdrawal timeline sought by Sadrists.
The pact, approved by both governments and now being bitterly debated in the Iraqi parliament, requires US troops to leave the streets of Iraqi towns by the middle of next year and to leave the country by 31 December 2011.
US forces will need Iraqi warrants to arrest people and U.S. contractors will be subject to Iraqi law.
Prime Minister Nuri al-Maliki obtained important concessions from the United States in months of gruelling negotiations, and has ridiculed the Sadrists for demanding a firm date for a US withdrawal, only to oppose it when he delivered it in the pact.
While the Sadrists have not made clear what their practical alternative to the pact is, they say US troops should leave Iraq immediately, not in three years. They also say they doubt the Americans will stick to the agreed timetable.
President Bush had long opposed setting a deadline. His elected successor, Democrat Barack Obama, has said he will withdraw combat forces within 16 months of taking office in January.
In Firdos Square, the Sadrist protesters erected an effigy of the outgoing U.S. president, carrying a briefcase with the words "The pact of subservience and shame." They hurled bottles at it, toppled it, tore it to pieces and set it on fire.
"I am with you in evicting the occupier any way you see fit," Sadr said in a message read out by a white-turbaned cleric to shouts of "God is Great" from the crowd.
Asked about the protests, US State Department spokesman Robert Wood said, "Iraq is really becoming a democracy, this is the kind of stuff that happens in democracies."
"We've compromised quite a bit, the Iraqi side compromised, and we think it is now time to bring this to fruition," he said, urging Iraq's parliament to approve the deal.