Washington (CNN) -- About 1,300 U.S. troops have been stuck at the Manas airfield in Kyrgyzstan because of the civil unrest there.

A U.S. military spokesman, who declined to be identified because of the sensitivity of the security situation, said the troops have been unable to move because of the suspension of U.S. military operations at the airfield.

The airfield in the former Soviet republic has been a transit point for troops and supplies moving in and out of the war zone in Afghanistan.

The spokesman said there are some refueling flights being run out of Manas but said that any decisions on future passenger flights will be made on a case-by-case basis.

The stranded troops include those coming home from Afghanistan and others going into the war zone. The spokesman said it is not known when the airfield will reopen, and it is not yet certain how the troops will be moved out.

Earlier this week, anti-government riots in Kyrgyzstan killed 76 people and forced the county's president to flee the capital, Bishkek.