President Barack Obama is set to announce on Wednesday the first phase of a withdrawal from Afghanistan that could see up to 10,000 U.S. soldiers leave the country by the end of the year.

Defense officials have been quoted as saying that Mr. Obama will call for an initial withdrawal of 5,000 troops, followed by an additional 5,000 by the end of 2011.

But White House Spokesman Jay Carney warned against media speculation on Tuesday, saying the president will explain how he will implement the strategy he outlined in December 2009 on drawing down American troops.

Mr. Obama announced the July start for the withdrawal in December 2009, when he presented his overall strategy for Afghanistan at the U.S. military academy at West Point, New York.

In his Wednesday night speech at the White House, President Obama is also expected to reaffirm the U.S. and NATO commitment to completely transfer security responsibilities to Afghan forces by 2014. The United States currently has about 100,000 troops in Afghanistan.

U.S. Defense Secretary Robert Gates said Tuesday the president has to take into account sustainability at home, both in Congress and among the American public, as well as conditions on the ground in Afghanistan.

Gates acknowledged concerns in the United States about Afghanistan, saying the American people are “tired of a decade of war.” He noted there are “a lot of reservations” in Congress about the war and the level of U.S. commitment.

Gates spoke Tuesday at the State Department, before heading to the White House with Secretary of State Hillary Clinton for consultations with the president about Afghanistan.

White House spokesman Carney said the president has remained focused on achieving his objectives in Afghanistan. He noted, however, that Mr. Obama's objectives there do not require defeating the Taliban, but rather “reversing the momentum,” which he says the military has been achieving.