The black box flight data and cockpit voice recorders from the hijacked plane that crashed into the Pentagon have been recovered.

The two black boxes are crucial to uncovering details about the doomed flight's last moments.

Pentagon spokesman Lieutenant Colonel George Rhynedance says the recorders are in the possession of the FBI.

Officials from the National Transportation Safety Board are providing technical assistance in reading any data they contain.

Rescuers have worked to shore up unsteady parts of the building but flames crept up what had been the roof at the crash site. The flare-up sent black smoke billowing hundreds of feet into the air over Washington.

Firefighters put out the blaze within 20 minutes. Authorities safely evacuated rescue workers who were clearing away debris inside the building, said Captain Scott Graham, head of the Montgomery County, Md., search and rescue squad.

Human remains pulled from the Pentagon are being taken to Dover Air Force Base in Delaware to be identified.

Members of Congress at the military office complex to watch the recovery effort say they were told by rescue officials that some of the fuselage of the airplane that slammed into the building remains intact in the wreckage.

"It hits you right in the pit of your stomach," Rep Ken Lucas said of the gaping hole in the building's side.