Detailed Instructions: In this task, you are given a text of many news articles seperated by special token "|||||". Your task is to summarize them.
Q: A clash between rival gangs in a prison in Mexico's north-western state of Sinaloa has left 29 inmates dead. 
  
 The killings brought the number of dead on another day of apparent drug-related violence to more than 40. 
  
 In the western state of Michoacan, 12 police officers died in an ambush by suspected drug cartel gunmen. 
  
 Michoacan and Sinaloa are home to rival drug gangs that are fighting turf wars and battling security forces. 
  
 Officials said 18 inmates had died in the Mazatlan jail in Sinaloa when members of one gang armed with pistols and an assault rifle forced their way into a cell-block holding prisoners from a rival gang and began shooting. 
  
 Eleven others had been stabbed to death as fighting broke out in other parts of the prison, they said. 
  
 Two police officers and a prison guard were wounded as they tried to stop the violence. Police and soldiers later regained control of the prison. 
  
 Continue reading the main story If we remain with our arms crossed, we will remain in the grip of organised crime, we will always live in fear President Felipe Calderon 
  
 Local media reports said some of the victims belonged to the Zetas drug gang, which has been fighting the Sinaloa cartel for control of smuggling routes. 
  
 The Sinaloa cartel is headed by Joaquin "Shorty" Guzman, Mexico's most wanted man. 
  
 Sinaloa state governor Jesus Aguilar warned last week of serious overcrowding at the prison, and asked that serious offenders be transferred. 
  
 Road blocked 
  
 Monday saw 15 police officers killed in clashes with suspected drug gang members. 
  
 Three officers were shot dead in the northern border state of Chihuahua when gunmen drew up alongside their two vehicles. 
  
 The ambush in Michoacan hit a federal police convoy as it was returning to Mexico City, officials said. 
  
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 Gunmen blocked the road with trucks and machine-gunned the police vehicles outside a school in the town of Zitacuaro. 
  
 Police say they killed and wounded some of the attackers, who fled. 
  
 Michoacan - President Felipe Calderon's home state - is the base of La Familia. 
  
 Last year the drug gang was blamed for the murder of 12 federal agents, whose tortured bodies were dumped on a highway in Michoacan. 
  
 At least 23,000 people have been killed in drug-related violence in Mexico since December 2006, when President Calderon ordered the army and federal police to combat the cartels. 
  
 In an article published on the presidency website and also in several newspapers, Mr Calderon defended his strategy. 
  
 "I am convinced that we would be in a much worse situation if we had not decided to take on the criminals," Mr Calderon wrote. 
  
 "If we remain with our arms crossed, we will remain in the grip of organised crime, we will always live in fear, our children will have no future, there will be more violence and we will lose our freedom." 
  
 On Friday, nearly 40 people were killed in two separate attacks blamed on drugs gangs - one in Ciudad Juarez on the US border, the other in Ciudad Madero in north-eastern Tamaulipas state. ||||| At least 29 inmates were killed Monday as rival gangs clashed inside a prison in a cartel-plagued Mexican state, authorities said. Three policemen guarding the prison were wounded. 
  
 In one attack, 20 inmates were shot to death when a group of prisoners opened fire on members of a rival gang inside the prison in Mazatlan, Sinaloa, state Public Safety Secretary Josefina Garcia told Radio Formula. One of the three wounded police was in serious condition, Garcia said. 
  
 The gang that initiated the attack killed 17 rivals and lost three of its own members. 
  
 An inmate who was wounded died later Monday at a hospital, said Martin Gastelum, a spokesman for the Sinaloa state prosecutors' office. He didn't say which gang the prisoner belong to. 
  
 The lockup in the Pacific coast city of Mazatlan was quickly brought under control and investigators found two pistols and an assault rifle inside, Gastelum said. 
  
 Gastelum said the killings were all at the hands of other prisoners. 
  
 Local media said those attacked were apparently members of the Zetas drug gang, which is battling the powerful Sinaloa cartel, but officials were unable to confirm that. 
  
 Hours later, eight more prisoners were stabbed to death by other inmates, said state Public Safety Department spokeswoman Angeles Moreno. She said police are investigating what sparked the violence. 
  
 Many of Mexico's most powerful drug traffickers hail from Sinaloa, a key smuggling corridor and cultivation area for marijuana and opiates. The northwestern state, and Mazatlan in particular, are rife with turf battles among drug gangs. 
  
 Mexico's drug gangs frequently try to break their members out of prison, by staging attacks from the outside or buying off prison officials. But there was no immediate confirmation Monday's shootings involved a prison-break attempt. 
  
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 Associated Press Writer Ricardo Gonzalez contributed to this report from Sinaloa, Mexico. |||||
A:
At least 29 inmates were killed yesterday as drug cartels clashed at a prison in Mexico's Sinaloa state. Three policeman guarding the prison were injured, and 20 inmates were shot to death when one gang forced its way into another cell block and opened fire on its rivals, AP reports. One wounded man died later in hospital and eight inmates were stabbed to death later in the day. The group attacked were members of the Zetas cartel, according to local media. In Michoacan state, headquarters of the La Familia cartel, ten federal police officers were killed in an ambush the same day. Police say the attackers blocked a highway with a truck and machine-gunned a police convoy when it stopped, the BBC reports. Several of the attackers were killed or wounded when police returned fire.