AFP/Mexico City

 Twelve inmates and nine guards were killed, up from 11 and six in the previous toll, said Jesus Rosso, the Durango state public safety secretary.

 He said the three additional guards were found to be dead after a roll call following the uprising at the prison in the city of Gomez Palacio. The additional prisoner died later of his injuries, he added.

 Rosso said the fighting broke out Tuesday when guards pulled the alarm after realising prisoners were planning to escape.

 As the alarm bells rang out in the facility, the inmates began shooting at the guard towers and the wardens’ office, he said.

 In the midst of the shooting, a group of inmates tried to escape through tunnels and over a back fence. Guards initially fired in the air before returning the prisoners’ fire directly. Troops deployed to the prison eventually put a stop to the attempted jailbreak and regained control of the facility.

 Rosso declined to specify what kind of weapons the prisoners were using or how they were obtained.

 He said the killed guards were unarmed, because when in contact with inmates they are not allowed to use weapons. Only agents posted outside the prison were allowed to use weapons, the secretary explained.

 Last Sunday, 137 inmates had been transferred to other jails and authorities had seized homemade weapons, cellphones, and appliances, he added.

 Mass jailbreaks have become a recurrent problem in Mexico In September, 131 inmates escaped through the front door of a prison in Piedras Negras, a city on the US border.

 In the last two years, 521 inmates have run free in 14 prison escapes while 352 homicides have been committed inside penitentiaries, according to the National Human Rights Commission.

 Prisoners often smuggle in drugs, weapons and even prostitutes, and gangs fight over control of the prison economy, according to the government office.

 A jailbreak at a prison in the northern state of Nuevo Leon in February saw 44 prisoners killed during fighting between two warring drug cartels.

 The commission said 60% of Mexico’s prisons are controlled by organised crime groups. Chronic overpopulation at the jails has sharpened the struggle between criminal gangs. Some 237,580 prisoners are packed in detention centers that only have the capacity for 188,147 inmates, a 26% surplus.

Mexico has 419 prisons - 13 controlled by the federal government and the rest managed by state and municipal authorities.