Two men were killed in a shooting Friday at a US Air Force base outside San Antonio, Texas, Brigadier General Robert Labrutta said.
They were found dead near two Glock pistols in a building with classrooms and office space, he said.
Air Force Times, an independent weekly newspaper, cited Defence Department internal communications that an airman may have shot a commanding officer.
"It appears to be a murder-suicide," James Keith, spokesman for the Bexar County Sheriff's Office, told dpa.
He said it was "too early" to confirm that the suspect was among the two dead.
A statement from Joint Base San Antonio confirmed two dead and said the scene was safe: "There are no indications that this was a terrorist attack."
Police first responded to reports of an active shooter at the base shortly before 9 am (1400 GMT). The sheriff's office initially confirmed two dead before details emerged.
The base was still under lockdown.
A military official at the Pentagon outside Washington confirmed a shooting incident with casualties at the base, which houses an Air Force basic training facility. Lackland Air Force Base is part of Joint Base San Antonio, a sprawling complex of Army and Air Force installations.