Iraq cleric says his forces could attack US troops

Any American troops remaining in Iraq after the end of the year will be attacked, according to Muqtada al-Sadr, the nationalist Shia cleric whose movement has previously fought to end the US occupation. He said that military operations by his Mehdi Army militia against US troops will be suspended to give them no excuse to remain beyond 31 December as was agreed by US and Iraq in 2008.

He threatened, in a statement on his website, that if there is not a full US withdrawal "the military operation will start again and with new approaches, and it will be very severe".

The continued presence of some US troops is being demanded by Kurdish and some Sunni leaders, highlighting big differences between Kurds, Sunnis and Shias in Iraq. The Kurds, in particular, are keen to see US troops patrol and mediate the swathe of territory in northern Iraq where Kurdish and Arab populations intermingle.

The Shia militia special units that have occasionally attacked US troops are drawn from the Sadrist movement; the evidence in the past has been that they are in practice controlled, trained, armed and paid for by Iran.

A US response to Mr Sadr's statement said: "We shall soon see whether the Promised Day Brigade and others affiliated with al-Sadr's organisation continue to conduct attacks against US forces and the Iraqi government."

There have been few attacks on the remaining 46,000 US troops in Iraq in recent weeks and no US soldiers were killed in August, though 14 died in June.

Iraq and the US have been talking about a force of 10,000 troops staying and US officials have leaked that it might be as low as 3,000 to 5,000.

Favouring the retention of some US troops is the mistrust between the three major Iraqi communities leading them often to fear and suspect each other more than they do the US, Iran or Turkey. Sectarian and ethnic divisions, always deep, became unbridgeable after the mass killing of 180,000 Kurds by Arabs in 1988-1989 and the civil war between Shias and Sunnis in 2006-2007.

The US wants to keep a residual force in Iraq as a symbol that it did not wholly lose out in the struggle for Iraq.