The US and Iraq are unlikely to come to an agreement on a long-term security pact before the 31 July deadline, White House spokeswoman Dana Perino has said.

The 31 July deadline is a self-imposed time-limit, so missing it would not have any impact on the legality of the US military's presence in Iraq.

But correspondents say the delay suggests that there are serious disagreements between the US and Iraq over the future of American forces in the country.

One of the sticking points in the negotiations has been the inclusion in the deal of a timetable for the withdrawal of US troops from Iraq.