BRUSSELS — After a dramatic security sweep late Sunday marked by the deployment of soldiers in the historic center of the Belgian capital, the authorities here announced early Monday that 16 people had been arrested in a joint police and military operation to try to head off what the prime minister earlier described as a “serious and imminent” threat of a Paris-style terrorist assault.

Belgian security forces conducted 19 raids in the Brussels region on Sunday and three in the southern town of Charleroi, Eric Van der Sijpt, a magistrate and spokesman for the federal prosecutor’s office, said at a late-night news conference. Backed by heavily armed soldiers, the police also sealed off at least two areas of central Brussels, including streets around the city’s medieval central square, the Grand Place, a major tourist attraction.

But the main target of the clampdown, Salah Abdeslam, suspected to be one of the gunmen in the Nov. 13 Paris attacks, was not among those arrested, Mr. Van der Sijpt said. The raids also uncovered no weapons or explosives, he added.

The Belgian news media reported Sunday that Mr. Abdeslam, a resident of the Brussels borough of Molenbeek whose brother was a suicide bomber in Paris, had been seen in the eastern city of Liège but then vanished again. Mr. Van der Sijpt declined to take questions on that or other aspects of the Belgian investigation into the links between the Paris attacks and Belgium.