The two at large suspects were dressed in military garb but are not believed to be U.S. service personnel, Lanier said.
One was a young white man in a khaki like uniform and the other was a black man in his 50s with a long rifle in an olive colored garb, she said.
Lanier said there were multiple fatalities at the scene but exact numbers were not immediately.
George Washington University Hospital has confirmed that a 60-year-old male was killed in the Navy Yard shooting Monday morning.
A spokesman said the man, whose name was not given, was dead on arrival to the hospital at around 9 a.m, about 40 minutes after the shooting.
The spokesman said the man was shot in the left temple and the wound was “not survivable by any stretch.”
The hospital said it was told to be prepared to take more victims of the shooting.