SAN ANTONIO -- A prison inmate was killed and 22 others were hurt following a riot Friday at a federal prison in Three Rivers, Texas.

Fifteen of the injured were hospitalized, San Antonio television station KSAT reported. Five of them were transported to University Hospital in San Antonio. Seven others were treated at the prison.

No prison staff members were injured.

Prison officials said two fights broke out at the prison around 7 a.m. There was no immediate word about what sparked the fights, which were brought under control quickly.

How the inmate died is still under investigation. Prison officials don't believe that guards used any potentially lethal force to break up the fight. His name has not been released pending notification of next of kin.

The prison is a medium security facility that houses 1,200 male inmates.

Three Rivers is located about 80 miles south of San Antonio.