Belgian police arrested two men suspected of planning an attack in the country after house searches on Friday evening, federal prosecutors said on Saturday.
The two, named as 33-year-old Nourredine H and his brother Hamza H, will appear before a judge on Saturday to determine whether they should be held in custody beyond an initial 24 hours.
The federal prosecution office said in a statement that police had carried out seven house searches in the region of Mons and a further house search in Liege. No weapons or explosives were found.
Brussels, home to European Union institutions and the headquarters of NATO, and Belgium in general are on a security alert level of three out of a maximum of four, a "serious" status with a "possible and probable" threat.