One man has been killed and another was seriously wounded after a shooting at a gate to the US National Security Agency headquarters.
The incident began shortly after 9:00 local time (14:00 GMT) when at least two people attempted to drive the vehicle into the National Security Agency section of the Fort Meade facility, according to a statement released by the Army base's public affairs office.
"We do not believe it is related to terrorism," FBI Baltimore spokeswoman Amy Thoreson said.
FBI investigators have been dispatched to the scene, where they are interviewing witnesses.
Fuller details were not immediately available, and multiple requests for information sent to the NSA have not yet been returned. Calls to the NSA were answered, but no information was provided. Calls to spokespersons for the Army were not picked up.
President Barack Obama had been briefed on the incident, according to White House officials.
Helicopter footage showed two cars - one a police vehicle and the other a black vehicle with no insignia - in a junction that had been roped off near the security gates leading to the NSA.
The cars appeared to have collided and debris was strewn across the intersection. A white cloth appeared to cover something beside the black vehicle.
The large Fort Meade campus, located in the suburbs of Washington, is home to about 40,000 military and civilian personnel, plus many members of employees' family.
The facility houses the US Cyber Command, the US Defense Information School, in addition to the NSA.
The NSA is a clandestine intelligence agency, charged with collecting and analysing electronic signals for US intelligence and counterintelligence purposes. The agency rose to prominence after Edward Snowden leaked thousands of the agency's documents in the Spring of 2013.
Local emergency responders say that the NSA police force is handling the incident, and local agencies are providing support.
Early this month the FBI arrested a man for firing shots that damaged the building from a nearby highway.