The growing number of young Europeans joining Al-Qaeda-linked rebels in Syria pose a "potential threat" for the European Union and its allies, France and Belgium warned Thursday.
"The phenomenon is particularly worrying," French Interior Minister Manuel Valls said alongside his Belgian counterpart Joelle Milquet.
Between 1,500 and 2,000 youths have gone to Syria where rebels are fighting to oust President Bashar al-Assad, they told a joint press conference.
Earlier this year, a report by King's College London estimated that 600 Europeans might have joined rebel forces in Syria since early 2011.
"For Belgians, it is between 100 and 150," Milquet said.
"For the French, it is slightly more than 400, of which 184 are currently in Syria," said Valls, adding that 14 had died, 80 had come back and 100 wanted to leave.
"When the conflict began in Syria, it was difficult to act because it was a matter of going to fight a regime condemned by all which made it difficult to say anything," Valls said.
Now the situation has changed, he said. "Most of those going say they want to fight in groups linked to Al-Qaeda."
For the moment, there appears to be no immediate threat but that does not mean "we can drop our guard because the jihadi groups have grown stronger and our nationals are becoming dangerous," he said.
France and Belgium are working together on the problem and have held meetings with Britain, Germany, the Netherlands, Italy, Spain and Denmark to coordinate a response.