Mexico's federal forces have taken over security and disarmed the entire municipal police force in a southern city after 43 students disappeared in what appears to be a gang-linked massacre involving police officers.
Monte Alejandro Rubido Garcia, the national security commissioner, said the Iguala police officers would be sent to a military base to undergo evaluations while investigators checked whether their guns were used in any crimes.
The federal police's new paramilitary-like police took over public safety in the city while the army would guard Iguala's entrances in the violence-plagued southern state of Guerrero, he said.
Authorities said it would take at least two weeks to get the results of DNA tests to identify the corpses found about 200 kilometres south of Mexico City.
Prosecutors said the Guerreros Unidos drug gang participated in the night of violence that left six people dead, 25 wounded and 43 missing.
Two gang hitmen linked to Iguala's municipal police force confessed to killing 17 of the 43 students in the same Pueblo Viejo district where the grave was found, authorities said.
The federal takeover came after President Enrique Pena Nieto vowed to punish those responsible for the mass disappearance.
"We will not rest until we find them," one father said of his missing son.
He declined to give his name out of fear.
Manuel Martinez, a spokesman for the families, announced plans for a nationwide march on Wednesday, which he vowed would "paralyse" Mexico.
The motive for what could be a mass killing of the students remained a mystery.
Many relatives said they were convinced their children were taken to punish the school, a special type of rural institution for poor students and a bastion of revolutionary political activity.
"What they do is they criminalise protest," said another father, who also declined to give his name. "They go after students, and the real delinquents are in the government."