Obama mourns 'yet another mass shooting'
President Barack Obama has mourned what he said was "yet another mass shooting" in the United States that took the life of American patriots.
Mr Obama promised to make sure "whoever carried out this cowardly act is held responsible."
He said the situation at the Washington Navy Yard about three miles from the White House was still unclear.
He said the victims were "courageous Americans" who knew about the risks of serving overseas, but would not have expected such "unimaginable violence" at home.
The White House said the president has been receiving frequent briefings about the unfolding situation by senior aides.