WASHINGTON (REUTERS) - Two people tried to ram their vehicle into the National Security Agency's entrance gates near Washington on Monday before guards shot one of them dead, officials said.

The two, who were dressed in women's clothes and may be transgender, tried to ram a sport utility vehicle into an entrance gate at the spy agency's Fort Meade, Maryland, headquarters, a senior US official said.

Their motive was not immediately known but officials said there was no evidence the incident was linked to terrorism. One official said investigators were looking into whether drugs were involved.

The pair failed to follow a police officer's directions to leave the gate area and barriers were put up. The vehicle accelerated toward an NSA Police car blocking the road at the base gate about 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 U.S. Attorney's Office in Maryland to determine whether federal charges were warranted

"The shooting scene is contained and we do not believe it is related to terrorism," the FBI said in a statement. "We are investigating with NSA police and other law enforcement agencies."

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.

Fort Meade said all personnel and residents on the base were safe.

Security at US federal installations has been under scrutiny in recent months after a number of incidents, including one in which a troubled veteran wielding a knife vaulted a fence and sprinted into the White House.

In another incident, a private civilian drone crashed into the grounds of the executive mansion, leading authorities to ban their use within the capital.

Most of the incidents have proved minor, but in September 2013, a lone gunman stormed a naval command centre in the Washington Navy Yard and killed 12 people before he was in turn slain by police.

The NSA specialises in code breaking and electronic surveillance, operating a global network of satellite surveillance, land listening stations and online data collection. It has been the focus of intense controversy since mid-2013, when former contractor Edward Snowden revealed the huge scope of its eavesdropping in a leak to the media. Washington has denounced Snowden's document dump and subsequent flight to Russia, but Obama's administration has agreed to reform some of rules governing data interception.

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