Mexican officials on Thursday called the 2014 disappearance of 43 students a state crime that was covered up by the government, in another damning assessment of the previous administration's actions regarding one of Mexico's worst human rights atrocities.

President Andres Manuel Lopez Obrador has pledged to reveal what happened to the students, who vanished in the southwestern city of Iguala in September 2014, having dismissed the previous government's version of events.