Mexican authorities have made four new arrests in the search for missing students.

Four members of the drug cartel Guerreros Unidos were detained for their alleged involvement in the kidnapping of 43 student teachers who are feared dead following protests in the south-western state of Guerrero last month.

Reports allege that the students were handed to the gang by local police. The students were last seen in police custody in Iguala.

“Two of the arrested men have said a large number of people were handed over to them,” announced Attorney general Jesus Murillo Karam. “At the moment they are giving their statements. The other two are lookouts, also from the criminal organisation. They confessed they took part as lookouts on the day of the event and at the moment, their statements have lined up with the testimonies of the first men arrested.”

The authorities have arrested more than 50 people in connection with the case.

They are still hunting for the Mayor of Iguala and his wife. Last week Mr Murillo Karam accused them of ordering the abduction.

The case has sparked national outrage and mass protests. One month on from the disappearance there is no sign of the missing students.

News of a new mass grave broke on Monday. The site in Cocula, is around 17 kilometres from where the students last were seen.

So far around 30 bodies have been found but forensic analysts are yet to identify any of the remains.

Since 2007 there have been around 100,000 deaths linked to gang-related violence.