Belgium is maintaining its highest alert level for the capital on Monday and closing schools amid a "serious and imminent" threat of terror attacks, Prime Minister Charles Michel said Sunday following a national security council meeting.
The rest of the country will be at a threat level of three on a four-tier scale.
Belgian security forces are searching for "several suspects" tied to recent terror attacks in Paris, a top official said Sunday, with residents in Brussels facing heavily-patrolled streets during a city-wide lockdown.
The city's subway system will remain closed Monday as well.
Interior Minister Jan Jambon said authorities are looking for Paris suspect Salah Abdeslam, who is believed to have entered Belgium immediately after a coordinated shooting and bomb rampage killed 130 people, as well as others linked to the Nov. 13 attacks claimed by Islamic State.
Salah Abdeslam, a Belgian national French police are searching for in connection with Paris terror attacks. (Police Nationale Handout Photo)
The Belgian prime minister had warned that "several individuals with arms and explosives could launch an attack" in one or more places in and around the capital.
Authorities told VOA's Jamie Dettmer that Michel's warning was based on "quite precise information," including the possibility that Abdeslam could be planning a suicide attack in the city.
Belgian media outlets reported Sunday that police had arrested on Saturday night four people, one possibly wearing a suicide belt. But Geert Schoorens of the federal prosecutor’s office said Sunday that he could “neither deny nor confirm” the reports.
WATCH: Heather Murdock reporting from Brussels
US: No credible information on more IS threats
The U.S. State Department says it has "no information to confirm" reports Islamic State plans to launch more attacks in France, the United States and elsewhere on Sunday.
The statement responded to a question about online activist group Anonymous, which said it had uncovered information about imminent plots that also included sites in Italy and Lebanon. The group said it forwarded relevant information to U.S. and British intelligence agencies.
One of the supposed targets is a professional wrestling event Sunday in the U.S. city of Atlanta. An FBI statement Saturday said it takes all threats seriously, but had no "specific or credible information of an attack at this time."
The State Department declined comment on whether it is taking extra security precautions at its facilities around the world, but said it is "already operating at a high level of security based on recent events."
Tanks guard tourist centers in Brussels, Belgium, Nov. 22, 2015, while journalists prepare to report on an event they hope will not happen.
Meanwhile, Belgian authorities raided nine homes in the city on Thursday, detaining nine people and seizing explosives and weapons. Some of the searches were in the Molenbeek neighborhood where Abdeslam lived along with his brother Ibrahim, who blew himself up outside a Paris cafe.
Authorities throughout Europe have been working to track down Abdeslam, who was last seen crossing into Belgium a few hours after the Paris attacks.
Some of the raids were connected to Bilal Hadfi, another terrorist who detonated an explosives vest that killed him outside a French stadium the same night.
The suspected architect of the attacks, Abdelhamid Abaaoud, was killed Wednesday in a police raid in a northern Paris suburb.
In separate developments Saturday, Russian officials said security forces killed 11 Islamic State militants and destroyed an arms cache in the North Caucus region, while authorities in Turkey said they arrested a Belgian citizen and two Syrians suspected of "aiding and abetting" IS terrorists. The Dogan news agency said the Belgian citizen is accused of carrying out reconnaissance for the Paris plot.
Victoria Macchi contributed to this report from Washington.