MEXICAN investigators looking into the disappearance of 43 teaching students have uncovered another clump of mass graves, authorities said on Thursday.

The discovery of a further undisclosed number of charred human remains came after a further four arrests in the case.

On Thursday, Murillo Karam announced the arrests, putting the total at 34, including 26 police officers.

The suspects led investigators to four new burial pits near the southern city of Iguala, where authorities unearthed 28 sets of badly burned bodies last weekend.

Forensic tests are still be carried out to determine if the bodies are those of the missing students, rounded up by police on September 26 following a day of violence in the town.

Prosecutors believe that the police handed the students over to a drugs gang with connection to Mayor Jose Luis Abarca, who is reportedly on the run with his wife.

Guerrero state prosecutor Inaky Blanco said he is asking the state congress to strip the mayor of the political immunity elected officials have under Mexican law.

Attorney general Jesus Murillo Karam said the city’s former police chief was also wanted for questioning.

Students at the Rural Teaching College Raul Isidro Burgos, in Tixtla’s Ayotzinapa neighbourhood, are taught to militantly defend the rights of the poor they teach.

They often engage in militant fundraising activities — such as bus hijackings — to provide cash for their free college where murals of Che Guevara, Marx, Engels and Lenin adorn the walls.