By Jessica Donati
KABUL (Reuters) - The United States is preparing to increase the number of troops it keeps in Afghanistan in 2015 to fill a gap left in the NATO mission by other contributing nations, according to three sources with direct knowledge of the situation.
The final numbers are still being agreed, but there will be at least several hundred more than initially planned, one of the sources said.
"If they hadn't done that, the mission would have lost bases," the source said.
Under the U.S. commitment, described as a "bridging solution" until other nations fulfill their pledges later in the year or the troops are no longer needed, Washington may provide up to 1,000 extra troops.
That figure was confirmed by all three sources, who said the final number was still under discussion and depended on when other countries stepped forward with their commitments.
The additional U.S. troops will be assigned to a 12,000-strong NATO force staying in Afghanistan to train, advise and assist Afghan forces through a new mission called Resolute Support, said the sources, who declined to be identified.
The bulk of Western combat troops are to leave the country at the end of this year when the mission officially winds up after 13 years of war against a stubborn Taliban and its al Qaeda allies.
President Barack Obama had announced in May that U.S. troop levels would be cut to 9,800 by the end of the year, by half again in 2015 and to a normal embassy presence with a security assistance office in Kabul by the end of 2016.
"There will be 9,800 troops, plus at least a few hundred above and beyond that," the same source said.
Of the 9,800, some 8,000 had been earmarked for the NATO force and the remainder for a separate anti-terrorism operation.
The move to increase the U.S. presence left in Afghanistan comes shortly after Obama approved plans to give the U.S. military a wider role to fight the hardline Islamist Taliban movement alongside Afghan forces after the mission expires.
(Reporting by Jessica Donati; Editing by Mike Collett-White)