Brussels will stay at the highest security threat level for another week over fears of an imminent terror attack, the Belgian Government said.
Authorities in Belgium and France were hunting for Belgian-born Salah Abdeslam, a key suspect in the Paris attacks on November 13, when gunmen and suicide bombers killed at least 130 people.
Belgian authorities have charged a fourth person in connection with the bloodshed in Paris, which was claimed by the Islamic State group.
Washington and Paris have stepped up their fight against ISIS, with France launching its first strikes from a newly deployed aircraft carrier in the Mediterranean and the US calling for more international cooperation against the group.
“Current information suggests that ISIl (another acronym for Islamic State), Al-Qaeda, Boko Haram and other terrorist groups continue to plan terrorist attacks in multiple regions,” said a State Department travel advisory.