The European Union should be prepared for returning jihadists if the so-called Islamic State (IS) is driven out of its Iraqi stronghold, Mosul, an official warns.
Security Commissioner Julian King said even a small number of militants would pose “a serious threat that we must prepare ourselves for”.
Iraqi forces say they have captured 10 villages near Mosul since beginning their long-awaited offensive on Monday.
As many as 5,000 IS fighters are believed to remain in the city.
Government troops, moving in from the south, are currently some 40km (24 miles) from the city, while Kurdish fighters are some 30km to the east.
The International Committee of the Red Cross has appealed to all sides to show their humanity as aid agencies brace for what they say could be the largest man-made humanitarian crisis of recent times.
Julian King, a British diplomat recently made the EU’s security commissioner, told Die Welt newspaper (in German) the threat of IS fighters returning to Europe after the fall of Mosul was “very serious”.
There were currently about 2,500 fighters from EU countries in the combat zones, he said.
However, he stressed it was “very unlikely that there would be a mass exodus of IS fighters to Europe”.
Similar cases in the past had shown, he said, that “only a few fighters come back”. But he added: “I don’t want to talk the risk down. Even a small number constitutes a threat.”
Some of the militants involved in the deadly IS attack on Paris last November had recently returned from Syria.