Mexican authorities looking for 43 students missing since late last month have found another mass grave, prosecutors say.
The students went missing in the town of Iguala and the mass grave was located in the nearby town of Cocula, prosecutors said.
Previously, a mass grave containing 38 bodies was found near Iguala. But tests on 28 of the sets of remains showed they were not those of the students.
Meanwhile two drug gang members were arrested on Monday on suspicion of direct involvement in the disappearance of the 43 students over a month ago, Mexico's top prosecutor said.
Authorities detained four Guerreros Unidos members, two of whom are believed to have helped carry out the crime that has shocked Mexico, Attorney General Jesus Murillo Karam said.
A total of 56 people have now been arrested in connection with the abduction of 43 male teachers' college students, in crime-plagued Guerrero state.
The students went missing after an attack by police and Guerreros Unidos cartel hitmen in Iguala that also left another six of their classmates dead and 25 wounded on September 26. Authorities still have not located the students.
Federal authorities accuse on-the-run Iguala mayor Jose Luis Abarca of ordering the attack to prevent the students from disturbing an event held by his wife as president of the local child protection institution.
A Guerreros Unidos leader said after his arrest that he had thought the students were part of a rival criminal gang. He therefore approved armed actions "in defence" of his territory.