The number of European fighters thought to be in Syria and Iraq has more than doubled in a year, new figures reveal.
Fighters from France have nearly trebled in the year to December, rising to 1,200, according to estimates from the International Centre for the Study of Radicalisation.
Governments have long been worried about jihadists returning from Syria and Iraq to carry out attacks in Europe.
The data was released just weeks after the Kouachi brothers carried out the worst terrorist attack on French soil- for more than half a century.
It is unclear where the pair were radicalised. But one of them was arrested in 2005, thought to be on his way to Iraq. After the Paris attack they claimed they were acting on behalf of al-Qaeda in Yemen.
After France, the UK and Germany had the biggest numbers of fighters estimated to be in Syria or Iraq.
Germany, which has seen anti-immigrant and anti-Islam protests in recent months, saw fighter numbers jump to 600 by December 2014, up 150% from a year earlier.
Belgium, meanwhile, has the highest proportion of its population thought to be fighting jihad, with 38 people in every million involved in Syria and Iraq.
This week the French government moved to tackle the problem of extremist groups like ISIL radicalising potential recruits using social media.
Anti-extremism think tank the Quilliam Foundation told Euronews last year that governments were at a loss over how to tackle ISIL’s “highly-intelligent and unprecedented” use of sites such as Twitter and Facebook.
The French government video, speaking directly to ISIL’s potential recruits, seeks to challenge the extremist group’s propaganda.
It says: “They tell you: ‘Sacrifice yourself for us and you will defend a just cause.’ In reality you discover it’s hell on earth and you die alone, a long way away from your home.
“They tell you: ‘Come and start a family with one of our heroes.’ In reality you raise your children amid war and terror.
“They tell you: ‘Join us and come and help the Syrian children.’ In reality you will be an accomplice in civilian massacres.”