The United States will determine in the next several weeks how many troops it will keep in Afghanistan as part of a residual force following the drawdown of most combat forces at the end of 2014, Defense Secretary Leon Panetta said on Monday.

Panetta said the top U.S. and NATO commander in Afghanistan, General John Allen, had submitted several recommendations for an enduring presence which were being reviewed by the Pentagon and White House.

"My hope is that we'll be able to complete this process in the next few weeks," Panetta told reporters flying with him to Australia. "I'm confident that we'll be able to get to the right number that we're going to need for the post-2014 enduring presence."

Panetta explained that the different options took into consideration the different types of missions for U.S. forces in the post-2014 period, including counter-terrorism, training Afghan forces and advising them.

"All of those are being carefully reviewed," Panetta said.