A shooting rampage at a U.S. naval base in the heart of Washington claimed at least 13 lives Monday, including the gunman, while another possible suspect remained at large, police said.
The shooting sparked a massive show of force as police and federal agents surrounded the Navy Yard, cordoning off streets only blocks from the Capitol.
Officials gave no indication of any link to terrorism, while police said the motive for the attack on the installation was unknown.
Washington D.C police chief Cathy Lanier initially said there were two other potential shooters on the loose, but her deputies later said one of these suspects had been cleared.
Police were searching for a black male aged 40 to 50 clad in an olive-drab, military-style uniform, she said.
With streets blocked off, Lanier warned residents near the Navy Yard that police were still conducting an "active search."
"Stay in your homes and stay out of the area," she said.
As the FBI took charge of the investigation, conflicting reports swirled online, and a clear picture of exactly what had happened at the naval installation had yet to emerge.
Earlier media reports had said a shooter allegedly barricaded himself in a room in a headquarters building.
Defense officials would not confirm or deny reports that the shooter may have served in the Navy.
It was unclear how one or more attackers could have penetrated the heavy security that surrounds the Navy Yard, which is located on the Anacostia River, less than 2 miles (3 kilometers) from the Capitol.
The description of the other potential shooter wearing a uniform raised the possibility that the attack was carried out by insiders who had military passes to enter the facility.
The police chief confirmed a Washington police officer was among those injured in the rampage, and hospital officials said he was in critical condition with wounds to his legs.