Aaron Alexis, 34, of Fort Worth, Texas, (pictured above) has been named as the gunman in the Washington Navy
A gunman who died after killing 12 people at a naval installation in Washington DC has been identified by the FBI as Aaron Alexis.
About a dozen others were wounded in the attack at Washington Navy Yard in the US capital.
Alexis was killed at the scene of the rampage, which began at around 8:20 local time (12:20 GMT).
Police were initially searching for two additional "potential" gunman but one has since been ruled out.
Alexis, a 34-year-old of Fort Worth, Texas, served full-time in the US Navy reserve from 2007-11, according to US military.
He was a petty officer 3rd class. It is not yet clear why he left the military or how he gained access to the facility.
Police responded to reports of two additional suspects in Monday's shooting, but have since cleared one of them, a white male in a tan short-sleeve military-style outfit.
Eyewitnesses at Washington Navy Yard: Gunman 'aimed
The US Senate buildings and nearby schools were temporarily placed on lockdown as a precaution.
At the White House, Mr Obama said he mourned "yet another mass shooting" and sent his thoughts and prayers to the victims.
Washington Police Chief Cathy Lanier confirmed on Monday afternoon that 12 people were deceased. Washington Mayor Vincent Gray told a news conference the attack had been "horrific".
One police officer was shot in the legs, a female civilian was shot in the head and hand, and another woman was being treated for a shoulder wound, she said.
At least three people, including the shot police officer, were brought to Washington Hospital Center by helicopter with gunshot wounds, said chief medical officer Janis Orlowski.
All three were originally listed in a critical condition but are expected to recover, according to Dr Orlowski.
Authorities said no motive was yet known for the shooting.
The FBI has taken control of the scene and the investigation, Chief Lanier said.
The shooting occurred at a building on the Navy Yard campus that serves as the headquarters for the Naval Sea Systems Command, which engineers, purchases, builds and maintains ships and submarines for the Navy.
A professional baseball game at Washington Nationals stadium blocks away scheduled for this evening has been postponed.