The bodies were found in the town of San Miguel Totolapan, which is in a region known for marijuana and opium production and as a shipment route for cocaine, said the Guerrero state investigative police director, Fernando Monreal.

This is the third time in less than a year that authorities have discovered mass graves in the Pacific coast state, which has seen a spike in violence since a turf war began between rival factions of the Beltran Leyva cartel after the December 2009 death of capo Arturo Beltran Leyva.

In November, authorities found a grave outside Acapulco with 18 bodies. They had been part of a group of 20 travellers kidnapped while visiting the resort city from neighbouring Michoacan state. Two men remain missing.

In May police discovered 55 bodies inside an abandoned silver mine on the outskirts of Taxco that had become a dumping ground for apparent victims of Mexico's drug violence.

Also on Tuesday, police found four bodies dumped along a highway connecting Acapulco to Mexico City. The four men had been shot to death, Guerrero state prosecutors said.

The bodies were found about 30 miles (50 km) from the spot along the same highway where four state police officers were ambushed and killed on Monday. The officers were guarding state police commander Humberto Velazquez, who was travelling in a different car and was unhurt in the attack.

Another four people, including a couple shot to death inside the hotel they managed in the coastal town of Atoyac de Alvarez, were killed on Tuesday in three separate attacks in Guerrero, prosecutors said.

More than 35,000 people have been killed in drug-related violence since the Mexican president, Felipe Calderón, launched a military offensive against the country's drug gangs shortly after taking office in December 2006.