US police have opened fire and one suspect is dead after two men dressed in women's clothing tried to ram their car onto the grounds of the National Security Agency outside Washington.
One police officer and a second suspect were hurt in the incident, said the National Security Agency's director for strategic communications, Jonathan Freed.
It was not immediately clear whether the suspects were shot or wounded when their car crashed into a police security vehicle.
A US official confirmed reports the men were wearing women's clothing.
An FBI spokeswoman said the incident at Fort Meade, the electronic eavesdropping agency's super-secure base in suburban Maryland, was not believed to be "related to terrorism".
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Officials said the drama was quickly contained and NSA headquarters staff were not at risk, but it will inevitably recall similar recent security incidents at federal sites.
According to Freed, a vehicle carrying two individuals was directed to turn back after it made an unauthorised attempt to enter the base.
Instead, the car accelerated toward an NSA vehicle blocking the road. Police opened fire, but the car crashed into the security truck.
"One of the unauthorised vehicle's occupants died on the scene. The cause of death has not been determined," Freed said, in a statement.
"One NSA police officer was injured and taken to a local hospital. The incident was contained to the vehicle control point."
The FBI has taken charge of the investigation and the White House said President Barack Obama had been briefed on the situation.
News footage from helicopters showed the crash-damaged police vehicle and a civilian vehicle outside a main gate, and an injured person being transferred to an ambulance.
The FBI said it has opened an investigation, joining other law enforcement agencies and deploying agents to the scene to gather evidence and interview witnesses.
"The shooting scene is contained and we do not believe it is related to terrorism," said Amy Thoreson, a spokeswoman for the FBI's Baltimore office.
"We are working with the US attorney's office in Maryland to determine if federal charges are warranted," she said.
About 11,000 military personnel and 29,000 civilians work at Fort Meade, which also houses the headquarters of the US Cyber Command and other military units.
