ATF agents gather in a parking lot. [Photo/IC]

The vehicle accelerated toward an NSA Police car blocking the road at the base gate about 20 miles (32 km) northeast of Washington. Officers fired at it when the driver refused to stop.

The vehicle crashed into the police car. One of the vehicle's occupants died at the scene, and the cause is undetermined, the statement said.

An NSA Police officer and the vehicle's second occupant were hurt and taken to a hospital. The Federal Bureau of Investigation is leading the probe into the incident, it said.

In a statement, the FBI said: "The shooting scene is contained and we do not believe it is related to terrorism."

NBC News, quoting unnamed sources, said the two were driving in a stolen car. A gun and drugs were found in the vehicle, a Ford Escape, the network said.

Television helicopter footage showed two damaged vehicles outside the gates to NSA headquarters, located just off a major highway linking Baltimore and Washington. Video showed at least one person in uniform being wheeled to an ambulance.

One of the vehicles shown was marked "Police" and had its hood up. The other, a dark vehicle, had front-end damage.

The FBI added it was working with the US Attorney's Office in Maryland to determine whether federal charges were warranted.