"The smell was intolerable," said Carlos Amezcua, the head of emergency services in Guerrero who participated in the recovery effort.

Among the dead was a recently kidnapped prison director, although the majority of victims of have not been identified.

Identifying bodies

Forensic examiners are trying to determine whether other human remains, clothing and shoes found in the shaft correspond to the bodies already found.

Authorities were tipped off about the mass grave in late May after they arrested an organised crime suspect in the nearby city of Iguala.

Nearly 23,000 people have died in drug-related violence since Felipe Calderon, the Mexican president, launched an army-led crackdown on drug gangs soon after he took office in late 2006.

Most have been killed in clashes between rival cartels fighting for drug smuggling routes to the United States, the No 1 consumer of Mexican narcotics.