Belgium raised the alert status for its capital Brussels to the highest level on Saturday, shutting the metro and warning the public to avoid crowds because of a "serious and imminent" threat of an attack.
A week after the Paris attacks carried out by Islamic State militants, of whom one suspect from Brussels is at large and said by authorities to be highly dangerous, the city was placed on the top level "four" in the government's threat scale after a meeting of top ministers, police and security services.
"The advice for the population is to avoid places where a lot of people come together like shopping centres, concerts, events or public transport stations wherever possible," a spokesman for the government's crisis centre said.
A statement on the centre's website said it had recommended closing the underground rail network until Sunday and the municipal transport authority tweeted that stations on the four main metro lines were closed "by order of the police".
The crisis centre website said it was calling on local authorities to cancel large events, urge people to avoid crowds, postpone soccer matches, close the Brussels metro for the weekend and stepping up the military and police presence.
The crisis centre spokesman declined to say what had led to the status change because investigations were proceeding.
“We cannot give more information... The work of federal prosecutors is still going on,” he said, adding the government was assessing what extra security measures to take. Soldiers are already on guard in certain parts of Brussels, including at the institutions of the European Union headquartered in the city.
Brussels is also home to the headquarters of NATO.