Twenty-one prisoners died Monday in a fight between inmates at a Mexican prison across the border from McAllen, Texas, officials said.

The Public Safety Department of Tamaulipas state, where the prison is located, said in a news release that the pre-dawn confrontation between two groups of inmates left 12 prisoners injured.

The cause of the riot and the inmates' deaths was under investigation. State authorities suspended the prison director and guards pending an investigation.

State and federal police, supported by army troops, took control of the state prison, located in the rough border city of Reynosa. Soldiers and police also ringed the outside of the institution as anxious relatives of inmates gathered outside to demand information, at one point kicking the prison gates.

Authorities did not say what sparked the confrontation, nor did the statement give details on the condition of the wounded, saying only they had been taken to local hospitals for treatment.

Last month, two riots at La Mesa state prison in the border city of Tijuana, across from San Diego, California, killed at least 23 people, including two inmates from the U.S.

La Mesa prisoners argued that officials weren't giving them food and water, but prison officials blamed troublemakers for the violence.