Washington ? The Central Asian nation of Uzbekistan has ended its agreement allowing U.S. military aircraft and personnel to use an air base that has been an important hub for American military operations in Afghanistan, administration officials said Saturday.

No reason was given by Uzbekistan for evicting U.S. forces from Karshi-Khanabad air base, commonly referred to as K2, was offered by either the State Department or the Defense Department. The Washington Post, which first reported the eviction notice, said U.S. forces would have six months to leave.

The New York Times reported Saturday on its Web site that a State Department official cited the abrupt action as a response to a United Nations operation to take hundreds of Uzbek refugees from the region.

More than 400 people who had fled to Kyrgyzstan after an Uzbek uprising in May were flown Friday to a refugee camp in Romania. The Uzbek government had sought their return.