One person has been killed and a second seriously wounded after two men tried to ram a car through a gate leading to the National Security Agency (NSA) headquarters, US officials have said.
The NSA said on Monday that one of the men died after a firefight ensued at Fort Meade in the US state of Maryland.
"Just after 9am [13:00 GMT] today, one person was killed and another injured when they attempted to drive a vehicle into the National Security Agency portion of the installation without authorisation," the agency said.
"NSA security personnel prevented them from gaining access to the installation."
A senior defence official said the two men were dressed as women. That official spoke to the Associated Press news agency on condition of anonymity because the official was not authorised to discuss an ongoing incident.
The car that rammed the police vehicle had been stolen Monday morning from a nearby hotel, said Mary Phelan, a police spokeswoman.
A guard shot at least one of the men and a gun and drugs were found in the vehicle, a Ford Escape.
An FBI spokeswoman later said that the incident at Fort Meade, a sprawling army installation near Baltimore, was not believed to be linked to terrorism and was contained.
A building on the NSA campus was damaged by gunfire earlier this month, with authorities capturing a man on March 3 who they believe fired that night on the NSA site, as well as earlier at several nearby places and two moving vehicles.
The suspect in that case, Hong Young, told police he heard voices directing him to fire on one of the occupied vehicles.