Mexico's President Enrique Pena Nieto has vowed to hunt down those responsible for the reported massacre of dozens of students in the southwest of the country that authorities said involved local security officials.
In a televised address on Monday, Pena Nieto said the federal government would identify those behind the massacre in the town of Iguala in the state of Guerrero, and make sure they face justice.
"We need to find the truth and make sure the law is applied to those responsible for these outrageous, painful and unacceptable acts," he said during his four-minute address. He did not take questions.
The news comes as the country's federal forces disarmed the local police and took over security of the town, where the 43 students disappeared on September 26 after clashing with police.
Monte Alejandro Rubido Garcia, the national security commissioner, said the Iguala police officers would be sent to another town to undergo evaluations.
A mass grave was found near the town over the weekend, full of charred human remains.
Some 22 local police have been arrested in connection with the violent incidents in Guerrero.
Guerrero's attorney general, Inaky Blanco, said on Sunday that 28 bodies have been found at the site so far, and it was "probable" that some of the missing 43 students were among the remains found in the graves.
Al Jazeera's Adam Raney, reporting from Ayotzinapa, where the students are studying, said that the parents of the missing studentswere demanding that their children be brought back alive.
He also reported that local gangs had threatened to release the names of politicians protecting them if the 22 detained police officers were not released.
Blanco said on Sunday that two gang hit-men had admitted killing 17 of the missing students with the help of security officials.
The likelihood of official involvement creates a major headache for Pena Nieto, who has sought to shift attention away from Mexico's gangland violence and onto a batch of economic reforms he has driven through Congress.
Angel Aguirre, the governor of Guerrero state, said he was certain the students were killed by gangs in cahoots with the police.
He added that he expected at least some of the bodies in the mass grave would be those of the students, but said tests still needed to be completed to make sure.
The fugitive mayor of Iguala, Jose Luis Abarca, is also being investigated for possible involvement in the crimes, as is the head of security for Iguala.
Blanco said the leader of a local gang known as the Guerreros Unidos conspired with security officials to carry out the killings.
Pena Nieto took office two years ago pledging to end a wave of violence that has killed about 100,000 people since the start of 2007. Though homicides have fallen on his watch, other crimes have increased, including extortion and kidnapping.
Guerrero, which is also home to the resort of Acapulco, has been one of the most lawless states in Mexico for years.