Authorities have confirmed to NBC News that at least four people have been killed and six have been injured after a gunman opened fire at the headquarters of the Naval Sea Systems Command in Washington D.C. Reports from the scene are still coming in, but a source told NBC that the shooter is currently cornered by SWAT officers. However, there are still conflicting reports coming from the scene. The Washington Post says that there are three shooters, one of whom is “down.”

Flights at Reagan International Airport were briefly grounded as authorities determine details about the shooter and rampage. According to military officials, at about 8:20 this morning, a gunman armed with an assault rifle began opening fire. It’s not clear who all of the victims are, but a military officials said that a naval security guard has been shot, and D.C. police say one of their officers has also been hit. We’ll post more updates as they become available …