An hours-long rolling gunbattle at a northern Mexico penitentiary left seven dead and 13 injured, authorities reported Wednesday.
Continuous automatic gunfire was heard late Tuesday at the prison in Ciudad Victoria, the capital of the border state of Tamaulipas.
The gunfire continued into the morning at the prison, which has been one of Mexico's most troubled.
The state security spokesman's office said three police officers and four inmates died in the shootouts, and six police and seven prisoners were wounded.
Inmates at the state prison somehow managed to obtain guns and began fighting authorities.
The prison has been the scene of shootings, smuggled guns, riots and escapes. Ciudad Victoria has long been dominated by the hyper-violent Zetas drug cartel.
A fight between prisoners at the same facility left three inmates dead in March. That clash followed a riot and mass escape through a tunnel that inmates built in a prison patio.
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Most of the prisoners have since been recaptured.
Inmates have frequently had access to guns in the prison.
During the March escape, at least one prisoner had a gun that he used to kill a passing motorist in a carjacking.
Police later found two assault rifles buried in a planter in the prison.
