Belgium maintained maximum security for the capital Brussels on Sunday, with a further review by intelligence, police and judicial services set for later in the day, Reuters reported. The Belgian crisis centre, which advises the government on security, said in a tweet that Brussels remained on the maximum level four, indicating a "serious and imminent" threat of an attack, while the rest of the country would at be at level three, meaning a possible and probable threat. Belgium put Brussels on maximum security alert on Saturday, shutting the metro and warning people to avoid crowds because of the threat of coordinated, multiple attacks by militants.