U.S. Defense Secretary Robert Gates announced on Wednesday extensions of duty tours for all active-duty Army troops in Iraq and Afghanistan from 12 months to 15 months.

"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," Gates told reporters at a Pentagon briefing.

U.S. Marine troops, National Guards and other reservists serving in the two war zones are not affected by the new order, he added.

"This policy is a difficult but necessary interim step," Gates said, noting that it was aimed to maintain the ongoing military buildup in Iraq.

U.S. analysts said the new plan will surely be unwelcome news to soldiers who have already had two and sometimes three deployments in Iraq.

However, there seems to be a good side for it, since Gates said the new policy also seeks to ensure that all active-duty Army units get at least 12 months at home between deployments.

"I think it is fair to all soldier that all share the burden equally," he said.

Gates acknowledged that the prolonged conflicts in Iraq and Afghanistan are further stretching the military and compounding burdens on their families.

He said "our forces are stretched, there's no question about that."

The latest decision reflected the painful situation the U.S. military is facing in order to meet U.S. President George W. Bush's goal to send 30,000 additional troops to Iraq and maintain that buildup.

According to Bush's plan, U.S. troop levels in Iraq will grow to more than 160,000 once the "surge" is completed.

News reports say U.S. commanders in Iraq want the increased level to be sustained at least through this summer.