WASHINGTON - The Pentagon is replacing its top general in Afghanistan as President Barack Obama tries to turn around a stalemated war.

Defence Secretary Robert Gates said Monday he asked for the resignation of Gen. David McKiernan. He said a fresh approach was in the U.S.'s best interest.

The move comes as more than 21,000 additional U.S. forces begin to arrive in Afghanistan, dispatched by Obama to confront the Taliban more forcefully this spring and summer.

Gates said new military leadership was needed to go along with a new strategy and a new ambassador.

He said the decision was in the best interest of national security.