Monterrey

Monterrey, Mexico (CNN) -- At least 38 people died during a prison riot in northern Mexico on Sunday, a security official said.

Inmates took a guard hostage as clashes broke out early Sunday morning at a prison in Apodaca, Nuevo Leon, state security spokesman Jorge Domene said.

Some prisoners also set mattresses ablaze, Domene said, sending a column of smoke rising above the facility.

Federal and state police had the situation under control later in the day, the state-run Notimex news agency said.

It was unclear what caused the clashes, which occurred in a part of the prison where most inmates were serving time for federal drug trafficking offenses.

Authorities had not indicated whether the dead were inmates or employees at the prison, or released details about how many people were injured in the fighting.

Dozens of people gathered outside the prison to find out whether their family members had died.

In May 2011, 14 inmates were killed and 35 people were injured in a fire in the prison's psychiatric ward.