Mexico has signed an agreement with the United Nations' top human rights official for technical assistance in its latest attempt to determine what happened to 43 missing students.

U.N. High Commissioner for Human Rights Michelle Bachelet called the case of the students from the teacher's college in Ayotzinapa "emblematic."

The former Chilean president said Monday that Mexico's government is obligated to find the truth and that the process would be an opportunity to make deep changes to its justice system.

Police seized the students in Iguala, Guerrero, in 2014 and allegedly handed them to a drug gang.

Mexican Foreign Secretary Marcelo Ebrard says the case is a priority for the government of President Andrés Manuel López Obrador, who created a truth commission to re-investigate the case in January.