The United Nations' human rights chief is calling on Mexico to allow a special panel of experts to investigate the disappearance of 43 students in September of last year.
Zeid Ra'ad al-Hussein, the world body's high commissioner for human rights, said Wednesday that Mexico City should allow experts from the Inter-American Commission on Human Rights (IACHR) to interview soldiers who were in the southern city of Iguala when the students vanished after a clash with police.
The government has said the students were illegally detained by police, who turned them over to the local drug gang Guerreros Unidos, which then allegedly killed them and burned their remains.
A group of independent experts assembled by the IACHR disputed that version, saying authorities knew who the students were from the minute they headed for Iguala, and at the very least did nothing to stop the attacks.
The experts have suggested that the attack occurred because students unknowingly hijacked a bus carrying illegal drugs or money. Iguala is known as a transit hub for heroin going to the United States.
Mexican Defense Minister Salvador Cienfuegos has refused to let anyone investigate his soldiers.
In a separate matter, commissioner Zeid also urged President Enrique Pena Nieto to set a timetable to relieve military forces of law enforcement duties. The troops have been deployed across Mexico since former president Felipe Calderon launched a massive crackdown on violent drug gangs in 2006; but the soldiers have been accused of committing human rights abuses.