Belgian prosecutors say they have arrested 16 people in raids Sunday night, after the city of Brussels spent the second day in a row on high alert.

Twenty-two raids were mounted, the prosecutors said — most in Brussels, and several south of the city. No explosives or firearms were recovered in the arrests, prosecutors say, and fugitive Salah Abdeslam, a suspect in the Paris attacks, was not among those arrested.

As we've reported, the Belgian capital has been essentially shut down since Saturday, after authorities said they received "concrete information" of a terrorist plot.

In a statement, the country's Crisis Center said the latest intelligence still points to a "serious and immediate threat." And after officials met on Sunday, they decided to close schools and universities on Monday. The metro will remain closed for a third day in a row.

Authorities fear that terrorists may be planning a Paris-style attack in Brussels.

NPR's Dina Temple-Raston reports that the rest of Belgium will remain on a lower state of alert.

"There will be a reassessment tomorrow afternoon, Prime Minister Charles Michel said," Dina reports.

Reporting from Paris, NPR's Peter Kenyon reports that the network of attackers may extend to Turkey. He filed this report for our Newscast unit:

"Prime Minister Charles Michel told Belgians that the threat level was raised because of what he called precise information about 'several individuals' planning an attack, possibly including suicide vests. Police discovered weapons at the apartment of a man arrested earlier in the poor suburb of Molenbeek.

"At least one of the Paris attackers, Salah Abdeslam, remains at large.

"In Turkey, police arrested a Belgian man suspected of scouting out sites for the Paris attacks. Turkish media identified the suspect as Ahmet Dahmani. He was arrested in southeast Turkey along with two other men who were suspected of trying to smuggle him across the border to Syria."

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