Several people have been injured and a suspect was taken into custody after a car crashed outside the US National Security Agency’s headquarters.
Gunfire rang out after the black SUV approached the facility in Fort Meade, Maryland, without authorisation.
There is no indication yet of any link to terrorism, officials said.
An NSA spokesman said it was unclear if the shots had been fired by law enforcement officers or the suspect, adding that the scene was now secure.
NSA officials said the injuries did not appear to be related to the gunfire.
They added that several people were taken to hospital from the US Army base, which is about 30 miles (48km) north-east of Washington DC, after Wednesday morning’s incident.
CBS News images showed the black sports utility vehicle with what looked like bullet holes in the front windscreen and its air bags appeared deployed.
It appeared to have collided into some NSA-stamped concrete barricade blocks outside the installation.
NBC News said its helicopter could see police surrounding a handcuffed man sitting on the ground.
The FBI’s Baltimore office said on Twitter that it had sent agents to investigate the incident, and that the situation had been “contained”.
Local emergency services also responded to the scene, and schools said they expected a delay as bus routes were affected by increased traffic.
The intelligence agency said on Twitter: “NSA police and local law enforcement are addressing an incident that took place this morning at one of NSA’s secure vehicle entry gates.
“The situation is under control and there is no ongoing security of safety threat.”
Another statement from the NSA public affairs office said “a security incident” happened at one of its checkpoints known as Canine gate at around 07:00 local time (12:00 GMT).
Maryland Congressman Dutch Ruppersberger tweeted that the reported injuries were not from gunshots.
US President Donald Trump has been briefed on the incident.
“Our thoughts and prayers are with everyone that has been affected,” said a White House spokeswoman, Lindsay Walters.
In March 2015, one person was killed and another seriously wounded after driving a vehicle up to the NSA’s gate, ignoring commands to stop.
News reports later suggested the two occupants of the vehicle may have been under the influence of drugs after attending a party.
Despite highway signage, it is not unusual for motorists to take a wrong turn and end up at one of the heavily guarded gates to the sprawling NSA complex, where armed federal officers direct them to turn around.