MEXICO CITY (AP) — An explosion occurred outside Mexico’s Attorney General’s Office on Thursday, injuring police as protesters demonstrating ahead of the anniversary of the 2014 disappearance of 43 students clashed with officers clad in riot gear.

Multiple police were injured by the explosion and loaded onto ambulances. Broken glass and blood were visible.

Members of a bomb squad cordoned off the area.

The protest was just one of a host of activities planned in advance of Monday’s 8th anniversary of the students' disappearances.

On Sept. 26, 2014, local police in Iguala, Guerrero abducted 43 students from a radical teachers’ college. They were allegedly turned over to a drug gang and never seen again. Three victims were later identified by burned bone fragments.

Last month, Interior Undersecretary Alejandro Encinas, who leads a truth commission investigating the case, called it a “state crime” and directly implicated the military, among other state actors including local and state police.

Former Attorney General Jesus Murillo Karam, who oversaw the original investigation into the disappearances, was arrested last month on charges of torture, official misconduct and forced disappearance. Last week, Mexico arrested a retired general, who had been in charge of the local army base in Iguala when the abductions occurred.

Dozens of student protesters arrived at the Attorney General’s Office aboard buses Thursday morning. Police with helmets and riot shields formed several lines of defense in front the entrances.

On Wednesday, activists had vandalized the exterior of Israel's embassy in Mexico City. Mexico is seeking the extradition from Israel of another key figure in the investigation of the students' disappearances.