At least one of 43 missing Mexican students has been identified among charred remains found in a landfill, raising new fears they were all slaughtered in a case roiling the government.
Authorities sent badly burned remains to an Austrian medical university last month after a police-backed gang confessed to killing the students and incinerating their bodies in the southern state of Guerrero in September.
"One of the pieces (of bones) belongs to one of the students," a Mexican federal official told AFP on Saturday on condition of anonymity, without providing further details.
If all 43 are confirmed dead, it would rank among the worst mass murders in a drug war that has killed more than 80,000 people and left 22,000 others missing since 2006 in Mexico.
The case has drawn international condemnation, highlighted Mexico's struggle with corruption and undermined President Enrique Pena Nieto's assurances that his security policy was bearing fruit.
The body's identification was confirmed by a spokesman for the families at a new protest Saturday over the case in Mexico City, where thousands waved black flags and called for Pena Nieto's resignation.
Family spokesman Felipe de la Cruz said that despite the information, relatives would continue searching for the 42 others.
The parents have rejected claims the students were killed, demanding that the government find them alive and leading their own searches around Guerrero.
"If they think that we will start to cry over the fact that one of our boys matches with DNA, they are wrong," de la Cruz told the crowd. "We will find the other 42."
The victim was identified as Alexander Mora, one of the students from the Ayotzinapa teachers college in Guerrero. His relatives received the news from independent Argentine forensic experts hired by the families who had suggested sending the remains to Austria.
- Few identifiable remains -
Authorities say the aspiring teachers vanished after gang-linked police attacked their buses in the city of Iguala on September 26, allegedly under orders from the mayor and his wife in a night of terror that left six other people dead.
The police then delivered the 43 young men to members of the Guerreros Unidos drug gang, who told investigators they took them in two trucks to a landfill, killed them, burned their bodies and dumped them in a river.
Despite the confessions, prosecutors stopped short of declaring the students dead, saying they would wait for DNA test results from Austria's Innsbruck University.
Prosecutors have warned that few remains had a chance of being identified.
Mario Patron, an attorney representing the families, said that while Mora's remains were found on the bank of a river near the landfill, it does not necessarily mean all the others were killed there too.
"The authorities must explain the whereabouts of the others," Patron told AFP.
The attorney general's office scheduled a news conference for Sunday to discuss the investigation.
- Pena Nieto vows reforms -
The case has turned into the biggest challenge of Pena Nieto's two-year presidency.
His approval rating has plunged to around 40 percent, the worst for a president in almost two decades.
Pena Nieto returned to Guerrero last week for the first time since the students went missing more than two months ago.
The case has put security back at the center of Mexico's agenda, shattering Pena Nieto's attempt to move the narrative away from the drug war to his internationally acclaimed energy and economic reforms.
The Mexican leader will host the Ibero-American summit in the eastern city of Veracruz on Monday and Tuesday.
Late last month, Pena Nieto unveiled a plan to enact constitutional reforms aimed at disbanding the country's notoriously corrupt municipal forces, replacing them with state agencies.
But security experts have voiced skepticism, saying the plan should tackle corruption at the state and federal levels too.