The twisted metal, crushed concrete and shattered windows convey some of the horror and carnage that took place at the Pentagon on Sept 11, 2001, when Al-Qaeda terrorists crashed American Airlines Flight 77 into the American military headquarters in Arlington County, Virginia.

The previously unpublished photo was released by the United States Federal Bureau of Investigation yesterday.

It is part of a set of 27 images taken by investigators at the Pentagon after the 9/11 attack.

The photos show firefighting crews battling the blaze that had ripped through the building and mangled fragments of the aircraft, as well as the Pentagon's scorched interior and exterior.

The American Airlines flight from Washington Dulles International Airport had been on its way to Los Angeles when hijackers diverted it to the Pentagon as part of the series of coordinated attacks against the United States by Al-Qaeda that day.

The aircraft struck between the first and second storeys of the Pentagon building, penetrating its three outer rings and creating a hole around 6m wide and 30m deep.

The attack resulted in 189 deaths, of which 125 were Pentagon employees.