Belgian police raided homes in Brussels on Tuesday and arrested 10 people on suspicion of operating a recruitment ring for the armed Islamic State of Iraq and the Levant (ISIL) group.
The federal prosecutor's office said in a statement that nine raids were carried out in four suburbs.
The statement said the police action has helped "to establish that several people have probably gone to Syria to join Islamic State."
Prosecutors said they had seized computer equipment and mobile phones.
A judge is due to decide later on Tuesday whether those arrested should be charged.
The raids are not linked to the deadly attacks in Paris last year.