MONTERREY, Mexico (AP) — An inmate riot that may have been staged to cover a breakout killed 44 prisoners Sunday, and the jail’s director and all guards on duty at the time have been detained, a security official said.

Nuevo Leon state public security spokesman Jorge Domene Zambrano said the riot broke out at about 2 a.m. in a high-security section of a state prison in the city of Apodaca outside the northern industrial city of Monterrey.

The fight between two cell blocks, each with about 750 prisoners, may have been staged as a cover for a prison break, he said. Domene said in counting the dead, officials discovered some prisoners missing, but didn’t know yet how many.

Forty-four people died before state police regained control about two hours later.

Investigators are looking into whether the fight was started by members of the rival Gulf and Zeta cartels, once the same organization. Their split two years ago has caused a spike in violence in the region around Monterrey, Mexico’s third-largest and once the country’s symbol of development and prosperity.

The prison had members of both gangs, who were normally separated, fueling theories that the 17 guards on duty could have been involved. The prison director, the director of security and a supervisor also are being held, Domene said.

The victims died from makeshift knives and blows, Domene said, adding that no firearms were found among the prisoners.