In an unannounced move, President Barack Obama is dispatching an additional 13,000 US troops to Afghanistan beyond the 21,000 he announced publicly in March, The Washington Post reported.

The additional forces are primarily support forces -- such as engineers, medical personnel, intelligence experts and military police -- the Post said, bringing the total buildup Obama has approved for the war-torn nation to 34,000.

"Obama authorized the whole thing. The only thing you saw announced in a press release was the 21,000," a defense official familiar with the troop-approval process told the daily.

The report, posted on the newspaper''s website late Monday, came as Obama weighs a request from the top US and NATO commander in Afghanistan, General Stanley McChrystal, for more combat, training and support troops, with several options including one for 40,000 more forces.

But the newspaper noted that the maximum number of US service members expected in Afghanistan by year''s end -- 68,000 -- would remain the same.