Adm. Mike Mullen, the chairman of the U.S. Joint Chiefs of Staff, speaks during a news conference at a U.S military base in the Afghan capital of Kabul on Saturday. (Rahmat Gul/Associated Press)

The U.S. military could double its presence in Afghanistan in 2009 with the deployment of up to 30,000 extra troops by next summer at the latest, the chairman of the joint chiefs of staff said Saturday.

"Some 20 to 30,000 is the window of overall increase from where we are right now. I actually don't have an exact number," Adm. Mike Mullen told reporters during a visit to the Afghan capital, Kabul.

On Friday, U.S. Defence Secretary Robert Gates approved the deployment of a 2,800-strong combat aviation brigade expected to arrive in Afghanistan in early spring.

Gen. David McKiernan, the commander of U.S. and NATO forces, has asked for at least 20,000 more troops to combat the escalating violence, particularly in eastern and southern Afghanistan.

U.S. president-elect Barack Obama has said getting more troops to Afghanistan is a priority.

The United States now has about 31,000 troops in Afghanistan, 14,000 of whom are participating in the NATO-led International Security Assistance Force, which currently includes about 2,750 Canadian soldiers.

During the recent federal election campaign, Prime Minister Stephen Harper reaffirmed that he will abide by a motion passed in the House of Commons that Canada would withdraw the bulk of its military forces from Afghanistan as scheduled in 2011.

With files from the Associated Press