A shooting rampage at a US naval base in the heart of Washington claimed at least 13 lives Monday, police said.
One of the dead was the alleged gunman, who the FBI identified as former serviceman Aaron Alexis, 34, of Fort Worth, Texas. His motives were still unknown, Washington police chief Cathy Lanier said.
Two others may still be at large after a shooting spree at the US Navy Yard in the heart of Washington.
Police and US federal agents descended on the area in a massive show of force, with streets blocked off, mere blocks from the Capitol buildings that house the US Congress.
It was unclear how a man armed with an assault rifle could have penetrated the heavy security that surrounds the Navy Yard, which is located on the Anacostia River, just a few miles from the White House.
US President Barack Obama on Monday condemned a "cowardly" shooting at the Washington Navy Yard, and vowed a "seamless" operation to administer justice to those responsible.
"As this investigation moves forward, we will do everything in our power to make sure whoever carried out this cowardly act is held responsible," Obama said.