The Office of the United Nations High Commissioner for Human Rights says Mexico's investigation of the 2014 disappearance of 43 students has been based on statements obtained through torture.
In a report released Thursday, the office says that 34 of the 129 people arrested in connection with the students' disappearance in the southern state of Guerrero suffered torture.
It says federal police, investigators and marines inflicted pain to obtain statements after the Attorney General's office took the case.
The U.N. is calling on Mexican authorities to throw out the material, which forms the foundation of the government's explanation of what occurred.
The government has said that the students were attacked by local police in Iguala, turned over to a drug gang, killed and incinerated at a garbage dump.