Mexican authorities searching for 43 missing college students have found human remains in an area of southern Guerrero state and were being tested to see whether they belong to the young men last seen in police custody a month ago, a government official has said.

Authorities made the discovery following information from four people arrested early on Monday, said the official, who spoke on condition of anonymity. The remains were found in Cocula, a town about 10 miles (16km) from where the students were last seen.

Mexico’s attorney general, Jesús Murillo Karam, confirmed the four arrests in a press conference but did not mention more remains or mass graves. He said some of those arrested could be members of the Guerreros Unidos cartel responsible for the disappearance of the students after an attack by local police. Two of the detainees said they received a large group of people around 26 September, the date the students went missing, Murillo Karam said.

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

The students, from a rural teaching college, disappeared after a confrontation with police in Iguala – a city about 80 miles (130km) south-west of Mexico City. Officials said the attack was ordered by Jose Luis Abarca – the mayor of Iguala – who is being sought, 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 on to a dumper 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 discovery, investigators had found 11 clandestine graves containing 38 sets of human remains in the hills surrounding Iguala. Initial DNA testing determined the bodies were not those of the missing students. Officials are waiting for results of further tests.

The crime has shaken the country and drawn international criticism and protests about the involvement of officials and police. Last week, Guerrero’s governor, Ángel Aguirre, stepped down amid heavy criticism of the state’s handling of the case and its political support of Abarca.

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

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