A mass grave have been found in Mexico, close to the town where 43 trainee teachers went missing last weekend after a protest turned violent.

After an anonymous tip-off, the remains of up to 20 people were discovered near Iguala in Guerrero state, 200 kilometres south of Mexico City. They have not been identified.

The students had travelled to the area to join a teachers’ rights protest.

Police reportedly opened fire on their buses; some students were last seen being taken away in police cars.

Six were reported killed in clashes.

Distraught relatives of missing students held rallies demanding information.

Twenty-two police officers were detained on Sunday, and face murder charges.

An arrest warrant was issued for the town’s mayor Jose Luis Albarca.

The authorities suspect police of links to drugs gangs. The extent to which police have been infiltrated by drugs cartels has been a major concern in Mexico and Guerrero state has become increasingly violent.