UPDATE (2:22 PM ET):
The most recent reports from the scene of a mass shooting at the US Navy yard in Washington, DC on Monday indicated that 12 people have been killed in the incident, with 15 reported shot.
Police confirm that one suspected gunman is dead at the scene.
"We potentially have two other shooters that we have not located at this point," said DC police chief Cathy Lanier at an afternoon press briefing.
The exact number of dead and wounded fluctuated in the hours following the shooting, which took place about three miles from the White House, starting about 8:30 a.m. EDT (1230 GMT).
The Washington D.C. mayor and the police chief said there were 12 fatalities in the shooting at the Naval Sea Systems Command, one of five such commands where civilians, military personnel and contractors build, buys and maintain Navy ships and submarines. About 3,000 people work there.
Numerous reports continue to say that law enforcement officials are still trying to determine the number of perpetrators involved and their possible whereabouts.
The Washington DC Police Department is tweeting official announcements and updates:
As the situation continues to develop, track updates on Twitter:
A shooting at a US Navy yard in Washington, DC, according to breaking reports, has left at least four people dead and 10 people wounded, with law enforcement officers among those who have been shot.
The gunman is said to be cornered within the complex, but the details remain hard to verify.
According to NBC News:
A gunman opened fire Monday at a Navy facility in Washington, authorities said. An initial report said at least four people had been killed and eight wounded.
Naval officials said that the gunman was on the loose.
SWAT officers swarmed the facility, the headquarters of the Naval Sea Systems Command at the Washington Navy Yard.
A naval security guard was among those shot and was hit in both legs, U.S. military officials said. Washington city police told WRC, the NBC affiliate in Washington, that one of their officers was also among those shot. It was not clear how many of the five others were civilian and how many were military.
NBC's Jim Miklaszewski reports on the U.S. Navy Yard in Washington, D.C. and shares the latest information. NBC's Kasie Hunt also joins the conversation.
Tim Hogan, a spokesman for Rep. Steven Horsford of Nevada, posted photos to his Twitter account of people tending to at least one person down on a street corner.
The Navy said on its Twitter feed that three shots were fired at 8:20 a.m. ET at the Sea Systems Command headquarters. Almost an hour later, the Navy still characterized the shooter as “active.” The military officials said that the gunman may have been armed with an AR-15, a military-style assault rifle.