Nine French citizens have been arrested in Chad, accused of making an unauthorised attempt to fly more than 100 children out of the country.
They include the head of a group called Arche de Zoe (Zoe's Ark) that had said it wanted to bring children from Sudan's Darfur region to France.
The nine were arrested at Abeche, near the Chad-Darfur border. A Paris court has launched a criminal investigation.
The French foreign ministry has condemned the incident.
France's Minister for Foreign Affairs and Human Rights Rama Yade, who had travelled to Darfur earlier this week, said the government had warned Zoe's Ark that it could be breaking the law.
"We know absolutely nothing about how these children were gathered. We don't know their origins, their nationality or the reality of their family situation. Taking them like this is in my view illegal and irresponsible," she told the AFP news agency.
Chadian President Idriss Deby Itno described the operation as "inhumane" and "unacceptable" and said those responsible would be "severely punished".
French government sources told the BBC that some 300 families in Europe may have paid a total of up to 1m euros ($1.4m) to charities in the hope of being able to adopt one of the children arriving from Chad.
Most of these families were French, and the remainder Belgian.
Some families had gone to the airport in Vatry, 120km (74 miles) east of Paris, in the hope of collecting the children as they arrived from Chad, a BBC correspondent in Paris says.
The UN children's agency, Unicef, said the operation "took place in violation of international rules".
Stephanie Lefebvre, secretary-general of Zoe's Ark, insisted the charity was acting out of compassion.
"There has never - I repeat - never been any question of us being an adoption agency," Ms Lefebre told AFP.
"These children were not intended for adoption. Our motives were simple: we just wanted to rescue them from death," she said.
She said families in France had offered to take the orphans into their homes, paying 2,400 euros ($3,440) to cover the charity's costs, Ms Lefebvre said.
The arrests took place after the authorities stopped several vehicles in which the children were being transported.
The children seemed shocked, and it was difficult to determine their names or where they had come from, a spokeswoman for the UN refugee agency, Annette Rehrl, told the BBC French service.
Chad's Interior Minister, Ahmat Mahamat Bachir, said nine French citizens had been arrested at Abeche airport and were being held in police custody in the town.
"They had no official authorisation. We have opened an inquiry," Mr Bachir told Reuters news agency by telephone.
They had planned to fly the children to France in a rented French charter plane, Mr Bachir said.
He said the 103 children were aged between three and eight, and included some Chadians.
The BBC's Stephanie Hancock in N'Djamena says many in Chad are stunned that anyone would attempt such an operation, especially if - as the Chadian government claims - the group had no proper authorisation.
In August, the French authorities issued a warning about the activities of Zoe's Ark, saying there was no guarantee that the children whom the group wanted to transport were actually orphans.