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

It comes after an anonymous tip-off. The remains were discovered near Iguala in Guerrero state, 150km south of the capital. The number of bodies and their identities are not yet known. Journalists and Human Rights Group stayed back while the police worked to identify the remains.

“We have made visual contact, from afar so as not to interfere. We are cooperating with the work that is being done. The place is inaccessible. The road is two kilometers and the place is very difficult to reach,” said Juan Lopez Villanueva from the National Commission on Human Rights.

Iguala was the site of violent clashes last weekend. Police fired on student protesters. Six were reportedly killed while some students were last seen taken away in police cars. Twenty-two officers are being held in connection with the incident. Mexico’s Chief Prosecutor Tomas Zeron has sent a team to investigate. “The Mexican state cannot permit such an indignant incident to go unpunished,” Zeron announced at a press conference. Arrests warrants have been issued for the mayor of Iguala, Jose Luis Albarca and his security chief.

Distraught relatives of missing students held rallies demanding information.

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.