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WASHINGTON, April 3 (Reuters) - The United States on Friday signed an agreement with Uzbekistan allowing nonlethal supplies for the war effort in Afghanistan to travel across Uzbek territory, a U.S. defense official said.

"The United States Department of Defense and the Uzbeki Ministry of Defense formally signed an agreement through an exchange of letters that establishes commercial shipping routes for nonlethal supplies," Pentagon spokesman Bryan Whitman told reporters.

Items covered by the agreement include food, medical supplies and building materials that would be carried via rail, road and air.

The United States and NATO have been seeking new supply routes to Afghanistan amid stepped-up militant attacks against convoys on their main land supply route through Pakistan.

Kyrgyzstan has said it will close a U.S. air base in Manas that has been a vital hub for supplies and reinforcements to Western forces in Afghanistan.

But Whitman said the door has not yet closed on American use of the Manas base.

"Kyrgyzstan has given every indication that they are willing to enter into discussions about the further use of Manas and that is ongoing," he said.

Concerns about supplies have mounted as the United States undertakes a military build-up in Afghanistan to a projected total of 68,000 U.S. troops this year from the current 38,000. The top U.S. commander in Afghanistan has asked for another 10,000 troops for 2010.

There are also about 32,500 troops in Afghanistan from other countries serving with NATO's International Security Assistance Force, according to the Pentagon. (Reporting by David Morgan, editing by Alan Elsner)

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