One of the premises targeted by police was at the Delaunoystraat in Molenbeek. Local police had received the support of special units in two of the four house searches.
The judicial authorities announced that no weapons, ammunition or explosives were discovered. The raids were part of a new investigation into terrorism, and are believed not to be linked to the Paris or Brussels attacks.
The Delaunoystraat was the place where a house was raided to find Salah Abdeslam last year. He was eventually apprehended in the nearby Vierwindenstraat.