Belgium police have detained 12 people as a pre-emptive measure against a possible terror attack. In total, 40 people, picked up from different locations in and around Brussels, are now in custody for questioning. City police conducted raids in 16 municipalities and 152 lock-up garages. However, Belgium's federal prosecutor said that no arms or explosives were found during the operation.

Belgian police are said to have recently been warned that a group of Islamic State militants had left Syria en route for Europe and are planning new attacks in Belgium and France, reported BBC.

The anti-terror operation was launched nearly three months after bomb attacks on Brussels. On March 22, as many as 34 people were killed after explosions in a Brussels airport and a metro station.