UN calls for Mexico probe into migrant train abductions
The UN human rights chief has urged Mexico to investigate the possible involvement of officials in the abduction of about 40 migrants.
Navi Pillay said the Central American migrants had been "abducted in highly questionable circumstances" from a cargo train in Oaxaca state last month.
They were reportedly taken by gunmen who stopped the train in Chahuites.
Mexico has said it is investigating, after initially saying the reports were unsubstantiated.
According to a statement from Ms Pillay's office, the train was first stopped by police and migration officials, who arrested 92 of the 250 migrants who had been stowed away.
The driver of the government-run train then took money from about 150 who re-boarded, the statement says, but he also allegedly warned of "more problems ahead" as he had not been happy with what they had paid him.
Shortly afterwards, gunmen seized the train, robbing the migrants and kidnapping 40 of them, including at least 10 women and a child.
Speaking on Friday, Ms Pillay called for "a thorough and transparent investigation of the alleged ill-treatment and abuse of the migrants by the [Mexican] Federal Police and the National Institute of Migration staff."
"The Mexican authorities need to ascertain whether or not any state officials ... were complicit with the criminal organisation that carried out the abductions and extortion, both in this and other cases," she added.
Ms Pillay said that, since the incident, "there has been no trace of [the migrants], and human rights defenders working with other members of the same group have been repeatedly threatened".
The Mexican Institute of Migration previously said that officials had boarded the train and detained a number of them, but that - after speaking to local and federal officials - there was no evidence that there had been a kidnapping.
But it has since said it is still investigating the incident.
Mexico's UN mission in Geneva had no immediate response to Ms Pillay's comments, according to AP news agency.