At least seven people were killed, including three police officers, in an operation to regain control of a Mexican prison where inmates had been smuggling in guns, authorities said.
Heavily armed local and federal police descended on the Ciudad Victoria prison Tuesday afternoon, kicking off a gunfight that raged through the night and into Wednesday.
Another 13 people were wounded in the shootout, including six police.
We had detected in recent days that there was tension between rival groups of inmates, said state security spokesman Luis Alberto Rodriguez, in comments to TV network Milenio.
We knew we might encounter resistance, and that resulted in shots being fired.
Outside the prison, a sustained hail of automatic gunfire could be heard as panicked inmates families gathered outside demanding to know what was happening.
The prison in the northeastern state of Tamaulipas has been hit by a string of riots and jailbreaks in the past.
In March, 29 inmates escaped, and, in a separate incident, a fire set by prisoners left three dead.
Tamaulipas, which borders Texas, has been racked by violence in recent years as drug cartels battle each other and the army over the lucrative narcotics trade to the United States.
Mexico’s prisons are frequently the scene of riots, revenge killings and escapes, and overcrowding is a chronic problem.