The country has the highest number of people per capita heading off to join Daesh fighters in foreign lands such as Syria.
The Belgian capital's underground transport system will be closed until Sunday afternoon, dozens of events have been cancelled and many public places closed.
But Saturday is proving challenging in other countries this week including the U.K. and Turkey.
In south London, armed police cordoned off Blackfriars Road, close to Southwark tube station and closed other roads. Three men travelling in a vehicle were arrested. Details were sketchy.
Jane Kinney for C4 however has tweeted "Met say they don't believe the ongoing incident at #Blackfriars to be terror related, will be reopening road shortly." There are some claims that the vehicle has a Brussels number plate.
The latest from Scotland Yard is "At 13:44hrs on Saturday, 21 November, officers stopped a vehicle on Blackfriars Road at the junction with St George’s Circus. The occupants of the vehicle - three men - were arrested on suspicion of theft of a motor vehicle. They currently remain in custody at a south London police station. Roads have now reopened."
But they deployed helicopters and armed units, and cordoned off a large area and many are asking why?
As Christmas approaches the city centre of London and other cities across the U.K. will be packed with shoppers from home and away. If 'terrorist jitters' keep people away shops will soon be complaining of slumping profits. But safety is paramount as well as going about our daily business in the usual way.
Three men have been arrested in Turkey Saturday and one is a Belgian-Moroccan man 'suspected of helping to pick targets' [a scout for the Paris attacks]. The other two men are Syrians who allegedly assisted his journey.
More as available