A rare rocket attack on the main U.S. base in Afghanistan early Sunday killed two U.S. troops and wounded six other Americans, including two civilians, officials said. Bagram Air Base, which lies 25 miles (40 kilometers) northeast of Kabul, is surrounded by high mountains and long stretches of desert from which militants could fire rockets. But such attacks, particularly lethal ones, are relatively rare, according to a report of The Associated Press. Two U.S. troops died and six Americans were wounded, including four military personnel and two civilians, said Lt. Cmdr. Christine Sidenstricker, a U.S. military spokeswoman. The top government official in Bagram, Kabir Ahmad, said several rockets were fired at the base early Sunday. A spokesman with NATO's International Security Assistance Force said that three rounds landed inside Bagram and one landed outside. The wounded personnel were taken to the main hospital on Bagram for treatment. ISAF said it wasn't known if any Afghan civilians living near the base were harmed in the attack.