US President Barack Obama has 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.
Obama bemoaned the fact that America was confronting "yet another mass shooting" and noted that those in the firing line knew the danger of serving abroad, but were now confronting peril at home.
The president noted that facts were still coming in from the attack, which police said caused "multiple" victims.
One gunman was killed and two other potential shooters remain at large, police said, after the attack in the naval installation, just a few kilometres across Washington from the White House.
