Thousands of followers of Shiite cleric Moqtada al-Sadr staged a mass rally in Baghdad on Thursday against US forces, as Iraqi leaders consider asking for an extended American troop presence.

The demonstration comes with just months to go before US forces must withdraw from Iraq, but senior American officials have said they hope Iraqi leaders will ask for troops to stay, while acknowledging the unpopularity of the soldiers.

At the protest in the mostly Shiite north Baghdad neighbourhood of Sadr City, named after father of the anti-US cleric, several groups of tightly-disciplined demonstrators wearing identical t-shirts emblazoned with Iraqi flags paraded in unison.

Waves of men clad in black trousers and caps bearing the words "I am Iraqi", marched in military-style formation, while others in the rally set fire to American and Israeli flags.

"We will not accept even one American soldier staying," said Adnan al-Mussawi, one of the demonstrators.

"Occupation has not benefited us at all, it is our religious duty to kick out every American soldier."

The demonstrators numbered several thousand according to an AFP estimate, but an official in the Sadrist headquarters in the southern Shiite city of Najaf said 100,000 were attending.

The office said the cleric arrived at the rally in a convoy of vehicles with the intention of delivering a speech, but was unable to get out because a mob of supporters flocked to his car.

An AFP journalist said a convoy of dozens of SUVs and pick-up trucks arrived at the demonstration, but could not confirm the Sadrist account in full.

Several protesters, who varied in age and in social class from the poor to heads of tribes, shouted slogans ranging from "No to the occupation!" to "The people want the occupier to leave!", referring to the widely held view of the US military as an occupying force in Iraq.

Some 45,000 American troops remain in Iraq, primarily tasked with training and equipping their Iraqi counterparts, although they must all withdraw by the end of the year under the terms of a bilateral security pact.

Earlier this month, Iraqi Prime Minister Nuri al-Maliki called for a national dialogue to gauge whether they should stay beyond 2011, and US Defence Secretary Robert Gates said on Tuesday that he hopes Iraqi leaders will ask US troops to stay beyond the deadline.

Acknowledging that American troops remain unpopular in Iraq, eight years after the US-led invasion that ousted Saddam Hussein, Gates said: "All I can say is that from the standpoint of Iraq's future but also our role in the region, I hope they figure out a way to ask."

Sadr, however, last month threatened to reactivate his feared Mahdi Army militia if the US troop presence were extended.

"We say to the Americans, you should get out," said Awouda al-Fartousi, a tribal leader.

"This is a peaceful protest, but if the Americans don't leave our country, we will pick up our guns. There should be a military and cultural resistance."