Now European Union nations have pledged to step up cooperation to keep more than 600 EU extremists fighting in Syria from veering toward terrorism upon their return home.

EU interior ministers said at a convention in Luxembourg on Friday that they plan to increase surveillance of social media, intensify collaboration with nations that border Syria like Turkey and urge the European parliament to approve legislation that would make ‘suspicious’ travel to the region more traceable.

This comes after Germany’s Interior Minister Hans-Peter Friedrich confirmed the presence of at least 50 German citizens fighting alongside Takfiri militants in Syria.

He also warned about the return of “ticking bombs” to European- a reference to the European extremists in Syria.

A recently published study reveals that between 2,000 and 5,500 foreign nationals are active in Syria. Senior counter-terrorism officials within the European Union are now confirming that over 600 of those nationals come from the EU countries.

The UK, Ireland and France are among the EU countries estimated to have the highest numbers of fighters in Syria.

French Interior Minister Manuel Valls admitted Friday that of that number at least 120 militants are from France.