Officials say a guard has been stabbed to death by inmates at a federal prison in Central California.

Merced County Sheriff Mark Pazin says 22-year-old Jose Rivera was taken to a hospital with stab wounds Friday afternoon and declared dead a short time later.

The U.S. Penitentiary in Atwater says the officer was stabbed by two inmates with homemade weapons.

An autopsy is planned and the FBI is investigating.

The prison is in the San Joaquin Valley about 64 miles northwest of Fresno.