An all clear has now been given at the US Army's Fort Lee base in the state of Virginia, following an earlier alert of an active shooter.
Fort Lee's Twitter account had carried a warning concerning the four-storey Cascom (Command Arms Support Command) HQ, Building 5020.
It said the "installation has been locked down until further notice", before the later all-clear was sounded.
Fort Lee's daily population is about 34,000.
It is situated about 25 miles (40km) south of Richmond, Virginia, and about 130 miles from Washington DC.
No further details have been given about the nature of the alert.
In April, three soldiers were killed and 16 wounded when army Specialist Ivan Lopez opened fire at the Fort Hood Army base in Texas before taking his own life.
The same base was also the scene of a 2009 rampage in which 13 soldiers were killed and 32 wounded by Maj Nidal Hasan.
In September 2013, Aaron Alexis, a 34-year-old former US Navy reservist, killed 12 people at the Washington Navy Yard.