General David Petraeus says the U.S. has made great progress in Iraq, but he warns that it could be lost in the months ahead.

During a 70-minute review of U.S. operations in Iraq, he said, "Progress does remain fragile and does remain reversible." He explained foes there like al-Qaeda are still formidable.

"This is an enemy who may be barbaric, who may carry out absolutely heinous activities, but a very, very savvy enemy, a very lethal and determined and learning enemy," Petraeus explained. "And we have to continue to learn, we have to continue to assess the situation on the ground."

General Petraeus also pointed out the positive signs in Iraq. He said the surge has knocked down the incidents of violence by 80 percent.