Belgium said it faced a serious and imminent threat of a Paris-style attack, and kept Brussels on maximum alert on Monday as security forces searched for militants thought to be at large in the capital.
Prime Minister Charles Michel, speaking after a meeting of security chiefs called to review the threat status, said the capital's metro, universities and schools would be closed on Monday.
For the rest of the country, a threat level of three on a four-tier scale would remain in place, Michel said. Brussels would remain at level four, meaning an attack was imminent, as it has been since Saturday.