The US Army has unveiled a detailed plan to replace troops serving in Iraq.
However, the acting chief of the army, General Jack Keane, has confirmed that the current US military commitments are putting a strain on the army.
The US is counting on allies to beef up the troop numbers
The US military has been under pressure to come up with what it calls a rotation plan for US forces in Iraq after a public outcry.
Some of the longest-serving troops currently there were recently told they would have to stay even longer because of the security situation.
The army has now unveiled its proposals.
The remaining elements of the Third Infantry Division, which was the first into Iraq and whose troops have had some of the most difficult missions since, is to be replaced in September by elements of the 82nd Airborne Division.
But it is a measure of the strain the army is under to meet the Iraq commitment as well as its other missions around the world that it will be calling up some extra reserve brigades and will be telling troops they could be serving in Iraq for up to a year.
General Keane told reporters at the Pentagon that the plan would stress the army, but he insisted it was sustainable.
However, he conceded that there would be additional problems if some of the foreign troops the Pentagon expects to make up to three divisions in the stabilisation did not materialise.
General Keane also defended the handling of the US raid in Mosul, which killed Saddam Hussein's sons Qusay and Uday, saying it was obviously the right decision to move in rather than wait.