One gunman has been killed while another may still be at large after a shooting that left an estimated 12 people dead at a U.S. Naval base in Washington, DC.
The city's police chief, Cathy Lanier, would not say how the dead gunman died. She also could not confirm the number of wounded, but said they are all expected to survive, including one police officer.
Lanier said the Federal Bureau of Investigation is leading the investigation. Security officers continue searching the Washington Navy Yard.
The city's mayor said there is no known motive for the shooting, but he said "there is no reason to think it is a terrorist attack."
At the White House, President Barack Obama said he is mourning "yet another mass shooting'' and called it a "cowardly act.'' He said the victims and their families need America's love and support.
The shooting took place at the Naval Sea Systems Command headquarters building, where about 3,000 people work. The Command is in charge of engineering, building, buying and maintaining ships, submarines and combat systems.
The Washington Navy Yard is located about two kilometers from the U.S. Capitol. The facility dates back to the early 1800s, and serves as the home of the four-star chief of the U.S. Navy, Admiral Jonathan Greenert.
Only security personnel are allowed to be armed on the base.
It is not clear how one or more gunman could have penetrated the heavy security that surrounds the Navy Yard, which is located on the Anacostia River. But some have raised the possibility that the attack was carried out by insiders who had passes to enter the facility.
As the incident unfolded Monday, emergency vehicles and law enforcement officers flooded streets around the complex, a helicopter hovered overhead, nearby schools were locked down, and airplanes at nearby Reagan National Airport were briefly grounded so they would not interfere with law enforcement and rescue helicopters.