Police are analysing bones found near the spot where missing hiker Esther Dingley went missing late last year.
A mountain runner raised the alarm around 2pm on Friday after discovering what he believed could be the remains of a body.
Spanish police went to the area but had to alert their French counterparts after discovering the spot was just over the border.
French police have now taken charge of the investigation to try to confirm they are human bones and if they are, who they could belong to.
Spanish police sources said they appeared to be human bones.
Police are analysing bones found near the spot where missing hiker Esther Dingley went missing late last year
British hiker Esther Dingley (pictured with her boyfriend Daniel Colegate) went missing November 22
A Civil Guard source said: 'A mountain runner has found what could be human bones just over the French side of the border at Puerto de la Glera.
'He called the Civil Guard who went to the area but after confirming it was on the French side of the border they called the French Gendarmerie who went to the spot and have now taken charge of things.
'They appear to be human remains but it will up to French police now to analyse them.'
Another Spanish source said it appeared '90 per cent certain' they were human remains.
Puerto de la Glera - Port de la Glera in France - is close to the 8,796ft Pico Salvaguardia summit where Oxford graduate Esther last made contact with her partner Dan Colegate around 4pm on November 22 last year.
Specialist officers from Spain and France have carried out several searches of the area around the Puerto de la Glera hiking trail.
Esther's partner claimed in a recent BBC interview he 'could no longer agree' with the idea she had suffered an accident.
He said: 'The search has been so prolonged and so intense, that as far as I'm concerned the probability of an accident is now less than the probability of a criminal act.'
Spanish Civil Guard officers resumed the search for Esther in mid-June and have been supported by a helicopter from a permanent base in the town of Benasque, where the missing hiker was staying before she vanished.
A Spanish court probe that opened after the Durham-born 37-year-old went missing on November 22 remains open.
Heavy snow and freezing temperatures have covered the mountains around Benasque where Esther Dingley was last spotted
