PARIS (Reuters) - Several suspected French Islamist militants have been arrested in northern Syria, including a man once convicted of running a jihadist recruitment network in France, a source close to the matter said on Wednesday.

According to French news channel LCI, the Syrian Kurdish YPG militia detained three men on Dec. 17.

“Several French (nationals) were arrested in northern Syria in the Hassakeh area, near the Iraqi border,” the source said, confirming the arrests.

The source added there were more than three French nationals stopped, including Thomas Barnouin, an Islamist known to French security services who is believed to have gone to Syria in 2014 to join Islamic State.

Barnouin was sentenced to five years in prison in 2006 for running a jihadi recruitment network in the southwestern Toulouse region, and was close to Mohammed Merah, a gunman who killed seven people in the area in 2012, including three Jewish children.

He is also close to brothers Fabien and Jean-Michel Clain, who were identified by officials as the voices in a jihadist audio message claiming Islamic State’s responsibility for attacks in Paris that killed 130 people in 2015.

The public prosecutor declined to comment. The French interior ministry said it could neither deny nor confirm the arrests.

The head of France’s DGSI internal intelligence agency, Laurent Nunez, warned in November that security services were still worried militants could continue to plan attacks in France from Syria and Iraq despite Islamic State’s loss of territory.

France’s foreign minister said on Dec. 9 that Paris estimated the number of French jihadists still in the region at about 500.

It is unclear whether those caught in Iraq and Syria will be returned to their home country, although French officials have said they expect all adults to face local justice.