Two men dressed as women smashed a stolen car into a police vehicle after they disobeyed commands at the closely guarded gates of the nation's spy agency on Monday, prompting police to open fire.

One of the men died, the other was injured and a police officer also was taken to a hospital. Details remained unclear hours later. Initial images from the scene showed emergency workers loading the uniformed officer into an ambulance. Nearby were a dark-colored SUV and an SUV emblazoned with "NSA Police," both heavily damaged.

A Maryland State Police cruiser sits at a blocked southbound entrance on the Baltimore-Washington Parkway that accesses the National Security Agency on Monday in Fort Meade, Md. Officials say one person is dead after a car with two people tried to ram a gate at the base. (Patrick Semansky/Associated Press) It was not known why the men wound up at the gate at Fort Meade, a sprawling military post that houses the National Security Agency, or why they did not obey orders from NSA police. Fort Meade is just off Interstate 295 between Baltimore and Washington.

The men were dressed as women, said a senior defence official who spoke on condition of anonymity because the official was not authorized to discuss an ongoing case. It also was unclear exactly what the men were wearing.

The NSA said in a news release that investigators have not yet determined how the man in the vehicle died, and the conditions of the wounded man and officer were not disclosed.

Stolen car

An agency officer gave the driver "routine instructions for safely exiting the secure campus," but the driver disobeyed them, the release said. The driver then accelerated toward a police vehicle blocking the road, and police then opened fire.

An FBI spokeswoman said earlier in the day that the incident was not believed to be linked to terrorism. The NSA said the incident was contained to the perimeter of the secure campus.

The car that rammed the police vehicle had been stolen Monday morning from a hotel in Jessup, Maryland, said Mary Phelan, a spokeswoman for the Howard County Police Department. She declined to name the hotel, citing the ongoing investigation, or release any further details, referring all questions to the FBI.

A strip of hotels, motels and other businesses is less than 16 kilometres from Fort Meade in Jessup.

The FBI is investigating and working with the U.S. Attorney's Office in Maryland to determine if federal charges are warranted, FBI spokeswoman Amy J. Thoreson said in an email.

It's not the first time someone has disobeyed orders at an NSA gate. In July, a man failed to obey an NSA officer's command to stop as he approached a checkpoint. The man drove away, injuring an NSA officer and nearly striking a barricade. He was later arrested.

NSA presence clearly visible

Earlier this month, police captured a man accused of firing at a building on the NSA campus. The man, who was also accused of shooting at vehicles, told police he heard voices.

Fort Meade also is home to the Defence Information Systems Agency and the U.S. Cyber Command. About 11,000 military personnel and about 29,000 civilian employees work on the property.

The NSA's presence is clearly visible in the area, with large satellite dishes and glass and steel buildings rising from the tree line. Chain link fences marked with restricted access signs and topped with barbed wire run along the perimeter of the campus.

Posted signs inform drivers of various exits for the NSA and Fort Meade, including one for deliveries, another for the visitors centre and one designated only for employees.

Jon Reinach, owner of Fort Meade Auto Centre, said people sometimes stop by his service centre asking for directions. Truck drivers sometimes also have to drop off their assistants at his shop because they don't have proper identification to get past security.

"A lot of people come in here trying to find their way to Fort Meade," Reinach said, adding that he's heard of people going through the wrong security entrance, but "usually they'll pull over to a waiting area and they usually do check out."