US troops will now serve up to 15 months in Iraq and Afghanistan instead of the usual 12-month tours under new Defense Department rules.

The move is designed to help the military supply enough troops for ongoing operations.

Soldiers will be allowed a minimum of 12 months at home bases upon return.

The extended tours apply to troops currently in Iraq and those about to be deployed, Defense Secretary Robert Gates said.

"Effective immediately, active army units now in the Central Command area [Iraq and Afghanistan] and those headed there will deploy for not more than 15 months and will return home to home station for not less than 12 months," he said.

There are currently 145,000 US troops in Iraq. Reinforcements are needed to help the so-called "surge" against the resistance that continues to deal heavy blows to Iraqi civilians and coalition forces.

"I think that what this recognizes, though, is that our forces are stretched," Mr Gates said.

"There is no question about that... What we are trying to do here is to provide some long-term predictability for the soldiers and their families".

US Marines - part of the US Navy - are not subject to the extended tours and will serve a seven-month tour overseas and six months at home, in rotation.

Photo caption

US troops in Iraq