Brussels, January 14 (RHC)-- As many as 5,000 European Union nationals have left the continent to join alongside terrorist militants fighting overseas, the head of the EU police agency, Europol, says. "We're talking about 3,000 to 5,000 EU nationals," Europol Director Rob Wainwright told British lawmakers on Tuesday, while referring to the number of foreign militants that had left from Europe.

The Europol chief also warned of a possible terrorism-related blowback if the mostly young men returned to their host European nations. "We're dealing with a large body of mainly young men who have the potential to come back and have the potential or intent and capability to carry out attacks we have seen in Paris in the last week," Wainwright said, adding: "It's the most serious terrorist threat Europe has faced since 9/11."

The remarks came after a wave of terrorist attacks in France left 20 people, including three assailants, dead last week. European countries have repeatedly expressed concern over the ISIL Takfiri group's influence across the continent. Authorities fear that the European militants will use their combat skills against their countries once they return home.