reporter sean carberry, who's in kabul. sean carberry, thank you so much for talking with us. what is known exactly about what happened? >> well, u.s. special operations forces and afghan forces were carrying out a clearing operation in zabul province which is one of the more unsecured provinces in the country and, according to afghan officials, when the troops were on their way back to the base from this operation, it came under attack by taliban militants. at that point, they called in for air support, and the air strike apparently hit the friendly forces, killing five u.s. troops and one afghan force. nato and u.s. officials have not officially confirmed that it was a friendly fire incident. they have indicated they're investigating that. however, afghan officials said the air strike hit the friendly forces, again, killing five u.s. and one afghan troops. >> woodruff: so it's not confirmed but sounds like the evidence points to friendly fire. is it known what type aircraft? >> reports are that it was a b-1 bomber, so this is not an apache helecopter or gunship or something