At least 10 decapitated bodies and 11 heads have been discovered in unmarked graves in a violence-plagued state in southern Mexico, authorities said.

The hands and feet on the corpses had been tied and the victims had clearly been tortured, officials said Tuesday.

Authorities found the badly decomposed bodies following an anonymous tip-off, a state police official told AFP. The remains had been wrapped in black plastic bags.

The mountainous region was last year the scene of armed clashes between rival drug trafficking groups who fought for control of the turf.

Guerrero state, a poor region where marijuana and poppies are grown, came to global attention following the September disappearance and presumed massacre of 43 student teachers.

That case, in which corrupt police are accused of handing the aspiring teachers over to hitmen from the Guerreros Unidos drug gang, has sparked nationwide outrage and caused a crisis for President Enrique Pena Nieto.