Gates suggested the current level of more than 160,000 soldiers could be cut to about 100,000 by the end of 2008. Bush said on Thursday about 30,000 troops might return by next summer.

Gates spoke as a White House report suggested Iraq's government has made little progress in meeting key military and political benchmarks set by the US.

Both Gates and Bush stressed that any reduction in troop levels would be entirely dependent on the success of their mission.

The defence secretary said:

"The whole situation and recommendations at this point are based on an analysis by the commander in the field, plus. . . the situation on the ground.

"One of the sad aspects of war is there is no script. That history hasn't been written yet."