Belgian police raided homes in Brussels on Tuesday and detained 10 people on suspicion of operating a recruitment ring for militant group Islamic State.
"Our investigation points to several persons having left for Syria to join Islamic State," Belgium's federal prosecutors said in a statement.
Prosecutors said they had seized computer equipment and mobile phones.
Belgium has one of the highest per capita rates of participation in militant groups such as Islamic State in Syria and Iraq.
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The US military has conducted airstrikes against Islamic State (IS) militants in Nigeria over the violent "targeting" of Christians.