Police carried out a series of 24 raids across Belgium overnight, detaining 21 people but failing to capture a primary target.
The searches were in connection with the investigation of the Nov. 13 Paris attacks that left 130 people dead.
Authorities seized about $27,651 in one particular raid, and all items from the searches are being examined, the Belgian prosecutor said in a statement. Some of the raids took place in Molenbeek, the Brussels neighborhood where some of the suspects in the Paris attacks lived, but the fugitive who’s being sought, attack suspect Salah Abdeslam, hasn't been located.
The country has been shut down since Saturday after Vice Prime Minister Didier Reynders revealed authorities were looking for "one and more individuals with weapons, explosives." The terror-threat level in Brussels has been raised to 4, the highest level.
"The threat is imminent, precise," Reynders said on Belgian television network RTL. "We're talking about possible attacks by several individuals, heavily armed."
Belgian Prime Minister Charles Michel said there was "threat of attacks with arms and explosives that could be launched in several locations at the same time," adding that the decision to raise the alert level was made based on "rather precise" information.
Sections of the city were closed off earlier Sunday by armed officers, with pedestrians told to stay away from the area and residents told to stay away from the windows.
Because of the high terror-threat level, schools and the subway system will be closed today, along with the U.S. Embassy.
Other transportation options such as trams, will operate on a limited basis, a statement from the U.S. Consulate said.