There could be as many as 30,000 foreign-born members of militant group Islamic State that could soon be returning to their home countries ready for radicalization and terrorism, according to the latest research.
European cities remain on high alert following the Paris attacks in November, in which 130 people died after European-born terrorists carried out bomb and gun attacks, and the lockdown of Brussels. And there are fears of further attacks.
Security services in Europe remain on high alert should members of Islamist terrorist groups, such as the so-called Islamic State, strike again in revenge for the Western airstrikes against ISIS in Syria and Iraq.
"The risks presented by returning jihadis will likely only increase over the coming year, as more of the estimated 30,000 foreign fighters who have joined Islamic State are expected to return to their countries of origin," analysis firm Verisk Maplecroft said in a report released in early December.