Twelve people have been detained following raids linked to last year's Brussels attacks.
Police raided 14 properties in and around Brussels on Tuesday and an investigating judge will decide later whether any of the detainees will be charged.
The federal prosecutor's office refused to give any further details.
On March 22 last year, 32 people were killed in twin attacks on Brussels airport and the subway system.
Belgium is still in a heightened state of security.