Mexican authorities have discovered some 60 mass graves and 129 bodies while they were searching for the corpses of 43 students who went missing from Iguala city, Guerrero state, in September 2014.
The students, from the Ayotzinapa Teacher Training College, disappeared after staging a protest against what they perceived an unfair hiring process for teachers, which favoured urban applicants over rural ones.
It is alleged they were abducted and handed over to the Guerrero Unidos drug cartel upon instructions from the then Iguala mayor, José Luis Abarca Velázquez, who feared the students' protest could disrupt an event being held by his wife, Maria de los Angeles Pineda Villa.
Prosecutors said the students were allegedly killed and their bodies burned on a pyre for 14 hours, making it almost impossible for authorities to identify the remains.
The new mass graves and the bodies, which investigators said are not linked to the students, were discovered during the ongoing investigation started in the aftermath of the students' disappearance, news agency AP reported.
Of the 129 bodies, 92 were men, 20 women and the rest undetermined, the attorney general's office said.
The students' disappearance led to violent rallies across Mexico where people protested against the country's widespread corruption and called for President Pena Nieto to step down.
Some 80 people, of whom 44 were police officers, have been arrested in connection with the students' disappearance, while Abarca was arrested and charged in January with the disappearance of the students.
In December 2014, an Austrian forensics lab identified the body of one of the students.