Guards have shot one man dead and seriously wounded a second after a car tried to force its way through the entrance gate of the United States NSA spy agency in Maryland.

One of the officials trying to protect the site at Fort Meade has also been hurt.

Reports say the FBI do not believe the incident is related to terrorism and that the men in the car were both dressed as women.

Television helicopter video footage showed two damaged vehicles outside the gates and at least one person in uniform being wheeled to an ambulance.

One of the vehicles was marked ‘police’ on the side and had its bonnet up. The other, a dark vehicle, had front-end damage.