While appearing on CBS's "Face the Nation," Gates said the main reason reports concerning al-Qaida have declined in recent months is the success of U.S. and coalition forces in fighting such militant forces.

"Well, the reason you don't hear much about al-Qaida is because our soldiers have been very successful, our soldiers and our Marines, in taking them on as have the Sunnis in Iraq themselves," Gates said.

Instead, Gates identified extremism in Iraq as the primary enemy.

"I think the enemy is extremism in Iraq, and it's Shi'a extremism in the form of the special groups and the Jaish al Mahdi, it's extremism in terms of al-Qaida. It's those who are not willing to participate in the political process and do so peacefully," Gates said. "Those are the enemy. And those who we are trying to help are those who are trying to build a stable government and a stable country."