At least 13 people were killed and as many as 10 others were wounded Monday morning during a shooting at the Navy Yard in Washington DC. One gunman is dead, and Metro police are seeking two other potential shooters.

DC police officers and FBI agents have responded to the scene, and at least one SWAT team has entered the building, according to reports on NBC Washington.

Two victims were reportedly found inside the Naval Sea Systems Command Headquarters, which houses 3,000 workers, and another was found on the building's roof. A fourth victim was found outside the facility, according to the Washington DC fire department.

UPDATE 3:40 pm: Aaron Alexis, a 34-year-old civilian contractor from Texas, has been identified as the gunman killed in Monday's shooting. Alexis reportedly used the ID of someone who used to work at the Navy Yard to gain access.

UPDATE 3:10 pm: From the New York Times:

Three weapons were found on the suspect: an AR-15 assault rifle, a shotgun and a semiautomatic pistol, the official said.

“It’s hard to carry that many guns, so there is some thinking that he may have taken some of them from security or whoever else he shot,” the official said

UPDATE: 2:54 pm: DC police has identified one of the men they were looking for and ruled him out as a suspect.

UPDATE 2:14 pm: Washington DC Mayor Vincent Gray said the death toll from today's shooting is at least 12.

UPDATE 11:41 am: CNN is reporting that two shooters "are down." The Associated Press and NBC News are reporting that a gunman is dead.

UPDATE 10:33 am: Reuters and the Associated Press are reporting that there were "several" fatalities, though it's still unclear how many. NBC's Pete Williams is reporting four fatalities with six others injured.

UPDATE 10:13 am: A senior Navy official told NBC Washington that four people were killed and eight were wounded. And the Washington Post is reporting there was more than one shooter:

Three shooters are involved in the Navy Yard shooting, a police spokeswoman said.

One of the shooters is “down,” police said, but two remain in a building on the grounds.

One of the shooters at large is dressed in fatigues. At least one has a long gun, police said.

UPDATE: 9:59 am: NBC Washington is reporting that there were at least 10 victims, including a security guard and a Metro police officer.

UPDATE 9:41 am: According NBC's Pete Williams, seven people have been shot, including two police officers. And according to the Washington Post, the shooter has barricaded himself in a room. The FAA has grounded all flights at DC's National Airport because of the shooting

UPDATE 9:30 am: There are now reports that a Metro Police officer has been shot.

The Washington Post is reporting that three people are in critical condition.

[Image via Tim Hogan]