There has been a series of incidents since March despite a much increased security presence on the streets
Belgium on Tuesday charged four people with involvement in terrorism after 15 early morning raids in the northern cities of Ghent, Antwerp and Deinze, the federal prosecutor's office said.
"Those persons have been indicted for participation in the activities of a terrorist group," a statement said.
"Some of them are suspected of recruiting people with a view to departing to Syria and joining Islamic State there," it added.
The prosecutor said no arms or explosives were found and the raids had no immediate connection with the deadly IS-claimed attacks on the Brussels airport and metro which left 32 people dead in March.
In all, 15 people were taken in for questioning initially, the statement added.
Some of them, who grew up in central Brussels and were known to the authorities, also took part in the November Paris attacks, which claimed 130 lives and left hundreds injured.
Belgium has been on its second highest terror alert since the Paris and Brussels attacks.
There has been a series of incidents since March despite a much increased security presence on the streets, the latest early this month when two police offers were stabbed in the Schaerbeek area of Brussels.
Prosecutors charged the suspect in that case with "attempted murder in a terrorist context and participation in the activities of a terrorist group."
Two months earlier, two policewomen were wounded in the southern city of Charleroi by a machete-wielding man who shouted "Allahu Akbar" (God is greatest).