Obama promised to make sure, quote, "whoever carried out this cowardly act is held responsible."
He said several people were shot Monday morning at the Washington Navy Yard about 3 1/2 miles from the White House, and some were killed.
He said the victims were "courageous Americans" who knew about the risks of serving overseas, but wouldn't have expected such "unimaginable violence" at home.
The White House says the president has been receiving frequent briefings about the unfolding situation by senior aides.
UPDATE: D.C. Metro Police Chief, Cathy Lanier says the initial call came in at 8:15 E.T. She says 1 of her officers was injured when he engaged a shooter at the Navy Yard. Lanier says 1 shooter is confirmed dead, and there MAY be two additional suspects that have not been located as of yet. She says there is no information suggesting those additional suspects are military workers, but says there IS information suggesting they may be wearing military type clothing. Lanier says multiple victims are dead.
UPDATE: Navy says death toll in Navy Yard shooting is at least 6.
UPDATE: President Obama is set to speak shortly. He's supposed to talk about the anniversary of the economy collapse, but we're monitoring to see if he makes comments on the Navy Yard Shooting.
UPDATE: WASHINGTON (AP) -- Federal law enforcement official: Shooter at Washington Navy Yard has died.
UPDATE: WASHINGTON (AP) -- Two officials say police are looking into the possibility of a second shooter at the Washington Navy Yard where several people were killed.
A Defense Department official and a law enforcement official spoke on condition of anonymity Monday because they were not authorized to discuss the ongoing investigation.
At least one gunman opened fire inside the Naval Sea Systems Command headquarters, where about 3,000 people work just miles from the Capitol.
Among the wounded was a D.C. police officer, according to a law enforcement official who spoke on the condition of anonymity because the person was not authorized to discuss an ongoing investigation.
At least 10 were wounded.
WASHINGTON (AP) -- A Defense Department official says several people have been killed and as many as 10 have been wounded in a shooting at the Washington Navy Yard.
The official spoke on condition of anonymity Monday because the official was not authorized to discuss the matter publicly.
The official also says the shooter is "contained" but not yet in custody.
Earlier in the day, the U.S. Navy said it was searching for an active shooter at the Naval Sea Systems Command headquarters, where about 3,000 people work.
The exact number of people killed and the conditions of those wounded was not immediately known.