An investigation is underway in east Wardak province in Afghanistan after a gun battle between US and Afghan forces left one US soldier, an American contractor, and three Afghan troops dead.<br /><br />Officials had initially thought the incident was the latest in a series of so-called insider attacks but NATO now says insurgent fire may have been a factor.<br />53 NATO personnel have died in what are called "insider attacks" where Afghan troops turn on coalition forces they are working with.<br />This latest attack brings the number of American service personnel killed in Afghanistan since the war started to two thousand.<br />Al Jazeera's John Terrett has more.
