Thirteen people, including one gunman, have died after a shooting spree at the US Navy Yard in Washington, officials have said.
Police were searching the Navy complex to track down the gunmen involved in the attack on Monday morning.
The Washington 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.
The dead suspect was identified by the FBI as Aaron Alexis of Fort Worth, Texas. Lanier told reporters that Alexis "was engaged in shooting with police officers" when he died.
"We have no indication of motive at this time," Lanier said.
Alexis, 34, received a general discharge from the Navy Reserve in 2011 after a series of misconduct issues, a Navy official said.
Al Jazeera's Kimberly Halkett, reporting from the scene, said there was an "enormous police presence" in the vicinity of the Navy Yard after the attack. Two helicopters were flying over the complex and roads were blocked.
Thousands of employees were initially told to stay inside the complex while multiple SWAT teams searched for the shooters.
The Navy said the first shots were fired at 8:20am (13:20 GMT) in the headquarters building of the Naval Sea Systems Command, where about 3,000 people work.
President Barack Obama pledged to do everything possible to make sure whoever was responsible for the attack was held responsible.
He said the victims were "courageous Americans" who knew about the risks of serving overseas, but would not have expected such "unimaginable violence" at home.
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.
PHOTO CAPTION
Media and emergency response personnel gather outside the US Navy Yard September 16, 2013 in Washington, DC.
Aljazeera