Two people including a suspected shooter were left dead at Naval Air Station Pensacola, a US Navy base in Florida, while others were taken to hospitals with injuries during an incident on Friday, authorities said.
The circumstances of the episode remained unclear.
An "active shooter" was encountered on the base on Friday morning, according to the Escambia County sheriff's office.
A few minutes later, the shooter was dead, according to the sheriff's office and the Navy.
"One additional fatality has been confirmed," the Navy said in a statement. "Unknown number of injured people being transferred to local hospitals."
Authorities did not provide further information.
On Wednesday, a sailor shot three civilians at the historic Pearl Harbor military base in Hawaii, killing two of them before taking his own life.
The Pensacola base, which is near Florida's border with Alabama, is a major training site for the Navy and home to its aerobatic flight demonstration squadron the Blue Angels. The base employs more than about 16,000 military and 7,400 civilian personnel, according to the base's website.