An estimated 50,000 supporters of the Iraqi Shia cleric Moqtada al-Sadr marched in Baghdad today against the planned long-term security pact extending the presence of military forces in the country.

Demonstrators chanted slogans and effigies of US President George W Bush and of US Secretary of State Condoleezza Rice were set ablaze along with several US flags.

US and Iraqi negotiators have reached agreement on a draft security deal which would govern the future status of US forces in Iraq after the present UN mandate ends in December.

The pact would replace a UN Security Council resolution authorising the US presence and give Iraq's elected government authority over the US force for the first time.

It must be approved by Iraq's parliament, and support is far from assured, even though Iraq won important concessions from Washington over the course of months of negotiations.

US officials have yet to explain the pact in public, but Iraqi leaders have disclosed its contents.

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 for them to stay, an apparent reversal for a US administration long opposed to deadlines.

It also describes certain conditions under which Iraq would have the right to try US service members in its courts for serious crimes committed while off duty.

In Washington, officials in the administration of US President George W Bush briefed members of Congress about the pact yesterday and sought reassure them that it protects US troops.

'I think there is not reason to be concerned,' Defence Secretary Robert Gates told reporters, adding that top military officials were happy with the protections in the pact.