NATO officials have said three American military personnel and a civilian have been killed in an aircrash in southern Afghanistan. It is not yet clear what cause the crash but a Taliban spokesman said its militants shot the aircraft down. NATO said the plane crashed about seven miles west of Qalat city in the southern province of Zabul. <br/><br/>The Taliban claimed its militants had shot down the aircraft around midnight local time. But the circumstances of the crash are still unclear and NATO says it is investigating the incidents.<br/>