Several people have been killed and others injured in a shooting at the US Navy Yard in Washington, officials say.
Police were searching the Navy complex to track down the gunmen involved in the attack on Monday morning.
Police chief Cathy Lanier said one shooter had been killed and that two other suspects – a white and a black male – were still at large.
She said the suspects were not believed to be military personnel but were wearing uniforms.
Earlier, reports said at least four people had been killed and eight others wounded. A police spokesman said a police officer and one other law enforcement officer were among those shot.
The police chief did not confirm the number of casualties, but said several people had been deceased.
The Navy said at least three shots were fired at 8:20 am (13:20 GMT) in the headquarters building of the Naval Sea Systems Command, where about 3,000 people work.
Todd Brundidge, an executive assistant with Navy Sea Systems Command, said he and other co-workers encountered a gunman in a hallway of their building on the third floor. The gunman was wearing all blue, he said.
“He just turned and started firing,” Brundidge said.
Flights at Reagan National Airport were temporarily halted to enable helicopters to transfer injured to hospital.
Janis Orlowski, a hospital spokeswoman at Medstar Washington Medical Center, said the hospital was treating two civilians and one police officer who were in critical condition with gunshot wounds.
She said the hospital expected more victims to arrive.
President Barack Obama made a statement on the shooting, pledging to do everything possible to make sure whoever was responsible for the attack was held responsible.
Naval Sea Systems Command builds, buys and maintains the Navy’s ships and submarines and their combat systems.
It is the largest of the Navy’s five system commands and accounts for a quarter of the Navy’s entire budget.
The Navy Yard complex is located 1.6km south of the US Capitol. It includes a museum and the residence of the chief of naval operations, among other buildings.