Thousands of people have marched in Mexico urging the authorities to take action over the unexplained disappearance of 43 students.
The youths, who went missing from Iguala, Guerrero state on 26 September, are feared to have been executed by drug cartels, after a mass grave full of human remains was found on the outskirts of the town.
The students went missing after they clashed with police, who shot at a bus that they claim had been hijacked by the youths. The clashes resulted in the death of two students and one person in a taxi.
Protesters carried photos of missing students and signs that read "Fascist government, assassin of teachers", Reuters reported.
Mexican President Enrique Pena Nieto vowed on Monday [6 October] to identify those behind the massacre and make sure they are held accountable.
Guerrero's attorney general, Inaky Blanco, said 28 bodies had been found at a mass grave site so far; he did not rule out the possibility that some could be the corpses of the missing students.
Blanco added that the leader of a local gang known as the Guerreros Unidos conspired with security officials to carry out the killings.
Protesters are also demanding the state's governor Angel Aguirre to resign.
Officials have discovered several mass graves around Mexico in recent years, some of which contained the bodies of migrants.
Hundreds of Central American migrants travel to Mexico each year and they are often killed by drug cartels which control the migrant-smuggling routes.
Last June, Mexican authorities found another mass grave containing at least 28 corpses near a ranch in the town of Tres Valles in Veracruz.