Number of foreign terrorist fighters in Belgium from 2013-2017, by region

The source adds: "According to Belgian authorities, a FTF is a Belgian resident (but not necessarily of Belgian nationality), aged 12 or more, that has joined or attempted to join a terrorist organisation abroad (thus individuals that joined Kurdish militias that are not listed as terrorist groups, for instance, would not be included in the FTF list). A “returnee” is an individual on the FTF list who went to Iraq/Syria and has left the fighting area. By including all residents, but also accounting for underage fighters, Belgium has rather inclusive criteria compared to some other countries. It also started compiling data on FTF in a systematic manner, earlier than any other European country."