At least 44 people died in a fight between rival gangs at an overcrowded prison in northern Mexico in a violent outbreak that authorities said could have been a distraction that allowed some inmates to escape.
Victims were beaten, stabbed and stoned when the fight broke out on Sunday. Inmates at the prison in Monterrey, about 140 miles (225 km) from the border with Texas, include members of Mexico's Gulf cartel as well as the feared Zetas cartel.
We can't rule out the possibility that some prisoners escaped, which also could be a motive if the fight started as a distraction, said Jorge Domene, security spokesman for the Nuevo Leon state government.
When we count the prisoners, and the number of confirmed dead, there are some missing, he said.
Investigators said corrupt prison guards may have been involved in facilitating the disturbance at the prison and authorities were holding all the prison officials for questioning, Domene told a news conference late on Sunday.
In recent years there have been a number of prison breaks in Mexico, sometimes with the aid of complicit guards.
Sunday's violence was the second deadly incident at a Latin American prison within a week. Desperate overcrowding in Honduras' prisons last week led to a massive fire in a run-down jail that killed more than 350 inmates.
The prison in Monterrey is, like many in Mexico, overcrowded as a result of the five-year-old drug war President Felipe Calderon has been waging against cartels.
It was not clear if the fight was between members of the Gulf and Zetas cartels, Domene said.
We hope that once the bodies are identified, we'll be able to say who was responsible for the attack, he said earlier in the day.
The prison held about 80 percent more prisoners than it was designed for, Domene said, adding many of the inmates were charged with federal crimes related to drug trafficking.
In Mexico, where prisoners held on federal drug charges are mixed with common criminals, the system is troubled by violence tied to the powerful drug cartels battling for control of smuggling routes along the U.S.-Mexican border.
During another fight between rival gangs in January in a prison in the northern part of the country, 31 inmates died and 13 were wounded.
Collusion between guards and prisoners is also a long-standing problem. In the most notorious example, collusion lead to the escape of Mexico's most wanted man, Joaquin Shorty Guzman, from jail in a laundry basket in 2001.
In 2010, more than 140 inmates escaped through the front gate of a prison in Tamaulipas state, helped by prison officials.
About 50,000 people have been killed in Mexico in the past five years since Calderon launched an army-backed offensive against drug gangs shortly after taking office.
Drug violence hit Monterrey, the wealthy capital of Nuevo Leon state, when the Zetas split off from their former employers the Gulf cartel and began fighting for control of drug trafficking routes and other criminal rackets in the city.
(Reporting by Adriana; Barrera and Elinor Comlay; Editing by Peter Cooney and Stacey Joyce)