Dozens of Ivorian soldiers held in Mali and accused of being mercenaries have been charged with attempting to harm state security and remanded in custody, judicial sources told AFP on Sunday.
But negotiations between Ivory Coast and Mali to obtain the release of the 49 soldiers were continuing, said a source close to the talks.
A Malian judicial source said a Bamako prosecutor charged the soldiers on Friday with an attempt to undermine state security.
They have already been detained for more than a month.
Another source close to the judge and an official at Mali's justice ministry confirmed the news to AFP.
Ivory Coast has denied the accusation and demanded the troops be released, saying they were reinforcements to the UN peacekeeping mission in Mali, MINUSMA.
Negotiations have started to free the soldiers, with Togolese President Faure Gnassingbe acting as a mediator.
A source close to the talks said they had made some progress but "stalled over certain points", which might explain the return to the judicial process.
"Justice will continue its work, but the negotiations will also continue," the source said.
The arrest of the soldiers after their arrival at Bamako airport on July 10 has sparked a diplomatic crisis between military-ruled Mali and its West African neighbour.
Diplomatic sources close to the talks say Mali is demanding that Ivory Coast acknowledge its responsibility in the affair and express its regrets for the deployment of the soldiers.
Bamako also wants Abidjan to hand over people who have been on its territory since 2013 who are wanted in Mali, said the sources.
Ivory Coast has rejected both demands and is preparing for extended negotiations to free its men, they added.
Ivory Coast says the soldiers were unfairly detained at Bamako's airport, after being sent to provide backup for the UN peacekeeping mission in Mali, MINUSMA. They say their role within the mission was "well-known to the Malian authorities".
Mali's military-led government however says they were detained after landing on a special flight without supporting documents and has described them as "mercenaries".