A female soldier has reportedly shot herself at Fort Lee in Virginia.
A US army base in Virginia was put on lockdown after reports of an "active shooter" on Monday but no one else was thought to be injured.
A report on Fort Lee's official Twitter feed said a "shooter incident" was active at 2.30pm GMT at the Combined Arms Support Command (CASCOM) headquarters.
The post was put on lockdown and staff were told to enact protocols immediately.
A statement on Fort Lee's official Facebook page said an "all clear" had been issued at 9.50am local time and the incident was over.
It continued: "Fort Lee first responders responded to a report of a female soldier with a gun inside the Combined Arms Support Command Headquarters at approximately 9am.
"Early reports indicate the soldier turned the weapon on herself and fired one shot, injuring herself. Her condition is not known at this time.
Agents from the US Army Criminal Investigation Command are on the scene and a Fort Lee spokesperson said officials were taking this incident "very seriously" and fully cooperating with the investigation.
Active shooter incident reported at CASCOM HQ, Bldg. 5020. All personnel enact active shooter protocols immediately. Post on lockdown.— U.S. Army Fort Lee (@ArmyFortLee) August 25, 2014
The Department of Homeland Security uses the term "active shooter" to describe someone actively trying to kill people, usually in a confined area, with no pattern of choosing victims.
The agency, housed in a four-storey building, provides training, logistics, transportation and works on sustainability strategy for the US armed forces.
Fort Lee, which also houses the US Army Women's Museum,has a daily population of around 34,000 people, including members from all branches of the military service, their families, government officials and contractors.
The base, which is the third-largest training site in the US, is about 130 miles from Washington.
A US Army spokesperson said no further information about the identity of the woman or her condition would be released until a press conference later on Monday.
She was taken to the Virginia Commonwealth University Medical Centre.