Six people have been detained in raids around Brussels in connection with the attacks on the city's airport and Metro system.
Belgian federal prosecutors said the arrests were made during raids in central Brussels, Jette and the Schaerbeek neighbourhood on Thursday.
Police found a large stash of explosives and other bomb-making material earlier this week in an apartment in Schaerbeek believed used by the suicide bombers.
Schaerbeek residents described hearing detonations during the police raids. It was unclear whether they were explosions or controlled blasts.