U.S. investigates attack on troops in Afghanistan

WASHINGTON (CNN) -- Military officials Friday were trying to determine whether an attack on a building housing U.S. Special Forces troops was in retaliation for the July 1 attack by U.S. aircraft on nearby villages that killed several civilians.

A U.S. Central Command official confirms the building came under fire at about 10 p.m. Thursday in the Afghan city of Tarin Kowt.

Tarin Kowt is the largest town in the area near the villages that were attacked when U.S. AC-130 gunships opened fire on what their crews said were anti-aircraft artillery sites.

This latest incident involved unknown enemy forces throwing hand grenades and using small arms against the building within the U.S. compound in Tarin Kowt.

The official tells CNN there were Afghan troops about 100 yards away from the building as part of a security perimeter and they returned fire. No U.S. or Afghan forces were hurt. It is not known if any enemy troops were killed.

U.S. Special Forces have been operating in the region for months and conducted ground reconnaissance that occurred prior to the July 1 attack.

Additional Special Forces units are being placed in the region under an agreement between the U.S. military and local Afghans as part of an effort to improve security in the region.