A clash between rival gangs in a prison in Mexico's north-western state of Sinaloa has left some 28 inmates dead.
Sinaloa's governor had warned of overcrowding at the Mazatlan prison
The violence came as dozens were killed on another day of apparent drug-related violence in Mexico.
In the western state of Michoacan, 10 police officers were killed in an ambush（埋伏，伏击） by suspected drug cartel（贩毒集团） gunmen.
Both Michoacan and Sinaloa are home to rival drug gangs that have been fighting turf wars（地盘站） and battling security forces.
Most of the prisoners killed in Mazatlan jail in Sinaloa were shot dead.
Members of one gang armed with pistols and an assault rifle（冲锋枪） had forced their way into a cell-block holding prisoners from a rival gang and began shooting, officials said.
Two police officers and a prison guard were wounded as they tried to stop the violence. Police and soldiers later regained（恢复，收回） control of the prison.
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.
Sinaloa state governor Jesus Aguilar warned last week of serious overcrowding（挤满） at the prison, and asked that serious offenders be transferred.
The ambush in Michoacan hit a federal police convoy as it was returning to Mexico City, officials said.
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 is the headquarters of La Familia, one of Mexico's most violent drugs gangs.
Last year the cartel 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 Felipe Calderon ordered the army and federal police to combat the cartels.
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.