France has asked Chad to return six French aid workers home after they were sentenced to eight years' hard labour for attempting to kidnap 103 children.
The French aid workers denied involvement in child-trafficking
French Justice Minister Rachida Dati requested that the six employees of the charity, Zoe's Ark, serve the sentences in France under a 1976 agreement.
The Chadian government has said any repatriation would have to be approved by the country's judicial authorities.
The aid workers have insisted they were trying to evacuate orphans from Darfur.
However, most of the children were found to be from Chad, which borders the western Sudanese region, and had parents who were still alive.
The case has sparked outrage in the former French colony in central Africa.
In a statement, Ms Dati said she had formally asked Chad for the four men and two women to be transferred to serve their prison sentences in their native country.
If Chad returns the aid workers, legal proceedings would be required in France to amend the sentences because the country has no punishment of hard labour.
Most children were not Darfur war orphans, as Zoe's Ark had claimed
Earlier, French President Nicolas Sarkozy, who is on holiday in Egypt, instructed diplomatic adviser to meet the families of the aid workers.
Afterwards, a lawyer for the families, Mario Stasi, said there was "every reason to hope" they would be transferred to French custody "in the coming days".
The six French nationals were found guilty of the "attempted kidnap of children, breaching their civil rights" on the fourth day of a trial that started on 21 December.
It also found the group guilty of "absconding without payment" of bills accrued in their attempt to fly the children out of eastern Chad town of Abeche.
According to the AFP news agency, the head of Zoe's Ark, Eric Breteau, and the Sudanese national, Souleimane Ibrahim Adam, were found guilty of a separate charge of using forged documents.
A spokesman for Zoe's Ark, Christophe Letien, told the BBC he was "stunned, sickened and confused by this judgement".
He said the fact the defendants were handed the same sentence for different responsibilities proved "that it was a totally unfair trial".
A Chadian and a Sudanese national who were also on trial were each sentenced to four years in prison. Two other Chadians accused in the child-trafficking case were acquitted.
Earlier this month, Chadian authorities said they had dropped the case against another 12 people initially held with the French aid workers. The 12 - including French journalists and Spanish flight crew - had already been allowed to leave Chad.
The United Nations children's charity, Unicef, has described the French charity's mission to fly children out of Chad as illegal under international law.
French officials also described Zoe's Ark's actions as "illegal and irresponsible".
Mr Breteau say he and his team genuinely believed they were rescuing orphans from Darfur and have accused their local contacts of duping them.
Some 200,000 people are estimated to have died in the conflict in Darfur between local rebel groups and militias allegedly backed by Sudan's government.
Pro-government Janjaweed militias are also blamed for forcing about 2m people from their homes - some of whom have crossed into Chad as refugees.