WASHINGTON, Oct. 13 (Xinhua) -- The United States is sending, in an unannounced way, 13,000 additional troops to Afghanistan, officials said.

    When U.S. President Barack Obama announced in March that he would be sending 21,000 additional combat troops to Afghanistan, he also authorized, in an unannounced move, the deployment of these support troops, The Washington Post on Tuesday quoted official sources as saying.

    The additional troops of support include engineers, medical personnel, intelligence experts and military police, and their deployment brings the total increase of U.S. troops in Afghanistan authorized by Obama to 34,000.

    As a result, the number of U.S. troops in Afghanistan will reach 68,000 soon, which would raise the total number of U.S. troops deployed to Iraq and Afghanistan above the peak during the Iraq "surge" that former President George W. Bush ordered in 2007.

    Analysts said the deployment of a large number of support troops also underscores the growing strain on U.S. ground troops, raising practical questions about how the Army and Marine Corps can meet a request from Stanley McChrystal, the top U.S. and NATO commander in Afghanistan, for a minimum of 40,000 more troops beyond what Obama had already authorized.