An activist group has said France's first air strike on Islamic State (IS) militants in Syrian territory killed 30, including 12 child soldiers.
The UK-based Syrian Observatory for Human Rights said Sunday's strike on an IS camp in eastern Syria had also wounded about 20 fighters, reports the BBC.
French president François Hollande said on Sunday six jets had destroyed the camp in the province of Deir al-Zour.
France had previously limited its strikes on IS to Iraqi airspace.
French defence minister Jean-Yves Le Drian said the raid had struck "an extremely sensitive site for [IS]", describing it as a "strategic hub" for militants travelling between Iraq and Syria.
He said the raid was carried out in self-defence, saying that France had evidence that foreign fighters were being trained in the camps to carry out attacks in Europe and in France specifically.
A teenaged former fighter told the BBC in June that he had been trained to fight for IS alongside mostly "15 and 16 year olds".
"There were even many as young as 13 or 14. Those are more eager to fight and wage jihad for the sake of God," he said.