Belgian authorities have raised the terror alert level in the capital to its highest. The move, officials have said, comes in response to what they called a "serious and imminent" threat.
Early Saturday morning, the Belgian news agency Belga, citing the Interior Ministry, said officials had raised the terror threat level to the highest possible.
"Following our latest evaluation... the center has raised its terror alert to level 4, signifying a very serious threat, for the Brussels region," the Belgian Interior Ministry said in a statement.
"The advice for the population is to avoid places where a lot of people gather together like shopping centers, concerts, events or public transport stations wherever possible," a spokesman for the government's crisis center said.
A statement on the center's website said it had recommended closing the underground rail network until Sunday. It also called on local authorities to cancel large events and postpone the weekend's soccer matches close to the Brussels metro. The municipal transport authority stated that stations on the four main metro lines were "closed by order of the police."
Authorities did not say what specifically prompted raising the threat level.
Belgium, and its capital Brussels in particular, have been at the center of investigations into the Paris attacks after it emerged that two of the suicide bombers had been living in the country.
Four people remain in custody in Belgium, prosecutors said Friday. They include one person linked to Paris suicide bomber Bilal Hadfi, one person detained in conjunction with the probe into the Paris attack, and the two men who are reported to have driven Salah Abdeslam from Paris to Brussels.
Salah Abdeslam is still at large. The 26-year-old is a presumed Paris attacker. His brother Brahim was among the dead suicide bombers.
Three people detained in Brussels are facing terrorism charges.
Meanwhile, the death toll from the attacks rose to 130 on Friday, French media reported.
av,das/sms (Reuters, AP, DPA)