French President Nicolas Sarkozy has condemned an attempt by a French group to spirit more than 100 children out of Chad on the grounds that they were orphans from Darfur in danger of being killed.
Mr Sarkozy called Chadian President Idriss Deby to discuss the case, his office said in a statement.
Chad's president has denounced the case as a "straightforward kidnapping" and promised punishment for anyone who tried to take the children out of the country.
At least 16 people, nine of them French, have been detained for questioning by authorities in Chad.
The nationalities of the 103 young children involved in the case are unclear. They are being cared for in the eastern Chadian city of Abeche. The children's ages range from one to 12, with most of them three to eight years old, said Rama Yade, a French human rights minister.
"The president of the Republic has condemned this operation, which he described as illegal and unacceptable," the president's office said.
Nine French nationals, six reportedly members of an aid group and three of them journalists, were arrested on Thursday.
Seven crew members of a Spanish charter company were also arrested.
The French TV station LCI reported yesterday that a Belgian pilot was the latest to be detained.
Mr Sarkozy said he inquired about the detained French nationals, particularly the journalists. Two of them were covering the operation and a third was reportedly present for personal reasons, according to the media watchdog group Reporters Without Borders.
Mr Yade said that France was fully cooperating with Chad's government in its investigation of the aid group, L'Arche de Zoe, or Zoe's Arc.
Zoe's Arc said it had arranged French host families for the children to save them from possible death in Darfur, where more than four years conflict has left more than 200,000 people dead and 2.5 million displaced - many to eastern Chad.
Officials were trying to determine the nationality and status of the children and whether they are orphans.
Initial questioning suggested many are Chadian.
Paris is "totally in agreement with President Deby's saying that this operation should not have happened," Mr Yade said.
The junior minister, along with other French officials, have claimed that they tried to dissuade the group from executing its plan.
Mr Yade said that the French had been aware of the group's plans for months, and advised Chadian authorities in July, insisting that "we did everything possible" to stop it.
Zoe's Arc had changed its name to disguise itself once in Chad, working under the name Children Rescue, Mr Yade said.
PA