's Foreign Minister, Hoshiyar Zebari, said a draft of the agreement hammered out after months of negotiations was now final and being reviewed by political leaders. Parliament would be given a chance to vote for or against it, but not to make changes.

“It is a peaceful demonstration, demanding that the occupier leave and the government not sign the pact,” Ahmed al-Masoudi, a Sadrist member of parliament said.

Iraqi authorities said the demonstration was authorized and security had been increased to protect the protesters, who were marching from Sadr's stronghold of Sadr City in the east of the capital to a nearby public square at a university.

The show of strength was a reminder of public hostility to the pact, which would give the US troops a mandate directly from Iraq's elected leaders for the first time, replacing a UN Security Council resolution enacted after the invasion in 2003.

The pact commits the US to end patrols of Iraqi streets by mid-2009 and withdraw fully from the country by the end of 2011 unless Iraq asks them to stay, an apparent reversal for a US administration long opposed to deadlines.