The officials said in an exclusive interview with Germany’s Der Spiegel magazine that they are most worried about the experience the German extremists have gained in Syria and the contacts they made there.
The officials also said they fear that the extremists, particularly given the usefulness of their passports, would return to Europe with terror missions.
Europe’s volunteer fighters can fly easily to Turkey without a visa and then easily cross the border into Syria.
The German Interior Minister Hans-Peter Friedrich confirmed that there were German-born gunmen who teamed up with militants inside Syria.
A recently published study revealed that between 2,000 and 5,500 foreign nationals are active in Syria. Senior counter-terrorism officials within the European Union have stated that at least 500 of those nationals come from the EU countries.
Pan-European police force, Europol, said in its annual EU Terrorism Situation and Trend Report released on April 25 that Syria was the “destination of choice for foreign fighters in 2012.”
The report cited the risk that the foreign fighters pose on Europe – after their return – through using new training and knowledge that they acquired in Syria for conducting terrorist activities.
Syria has been gripped by unrest since March 2011, and many people, including large numbers of government forces, have been killed in the violence.
Damascus says the chaos is being orchestrated from outside the country, and there are reports that a very large number of the militants are foreign nationals.