Mexican authorities searching for 43 missing college students have found human remains in a new area of southern Guerrero state and are testing to see if they belong to the young men who last were seen in police custody a month ago, a government official said Monday.

Authorities came upon the new location based on statements from four people arrested early Monday, said the official, who spoke on condition of anonymity because he was not authorized to speak to the press. The new remains were found in Cocula, a town about 17 kilometres from where the students last were seen.

Attorney General Jesus Murillo Karam confirmed the four arrests in a press conference but made no mention of more remains or mass graves. He said some of those arrested could be members of the Guerreros Unidos cartel who are believed responsible for abducting the students after an attack by local police. Two of the detainees said they received a large group of people around Sept. 26, the date the students went missing, Murillo Karam said.

Investigators were trying to confirm their statements. Mexico now has a total of 56 people in custody in the case.

The students from a rural teachers college disappeared after a confrontation with police in Iguala, a city about 130 kilometres southwest of Mexico City. Authorities say the attack was ordered by Jose Luis Abarca, the mayor of Iguala who is being sought by officials, along with his wife and the city's police chief.

Murrillo Karam has said the local officers took the students to a police station and then to Cocula. At some point, they were loaded aboard a dump truck and taken, apparently still alive, to an area on the outskirts of Iguala, he said.

Mexican authorities have mounted searches for the students, spurred by increasingly violent demonstrations that included the burning of Iguala's city hall by protesters last week. Before Monday's new discovery, investigators had found a total of 11 clandestine graves containing 38 sets of human remains in the hills of Pueblo Viejo in the municipality of Iguala. Initial DNA testing of the remains determined the bodies were not those of the missing students and officials were waiting for results of second round of tests.

The crime has shaken the country and drawn international criticism and protests for the involvement of officials and police. Last week, Guerrero Gov. Angel Aguirre stepped down under heavy criticism of the state's handling of the case and its political support of Abarca.

Rogelio Ortega Martinez, a sociologist and former university administrator, was named interim governor on Sunday.

The 59-year-old Ortega previously was secretary-general of Guerrero's state public university. Ortega is a former social activist and the son of a rural schoolteacher. He has close ties to the state's ruling Democratic Revolution Party.