Guards shot one man dead and seriously wounded a second when they tried to ram a vehicle into the entrance gate at the Fort Meade, Maryland, headquarters of the National Security Agency, news reports said.

Federal law enforcement officials told Reuters that two people in a car tried to ram the spy agency's gate and initial indications are that at least one was seriously injured. The motive was unknown but the incident was not related to terrorism, the officials said. The FBI is investigating.

One federal law enforcement official told Reuters the incident appeared to be a local criminal matter.

White House Principal Deputy Press Secretary Eric Schultz said: "The President has been briefed on this morning's incident at the National Security Agency and will be updated as appropriate."

NBC, quoting sources, said the men, disguised as women, were in a stolen car. A guard shot at least one of the men and a gun and drugs were found in the vehicle, a Ford Escape.

The NSA is investigating the incident, which occurred about 20 miles (32 km) northeast of Washington, NBC said.

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 hood up. The other, a dark vehicle, had front-end damage.

An NSA spokeswoman had no immediate comment. Spokesmen for Fort Meade and Anne Arundel County Police referred questions to the spy agency.