BRUSSELS —Belgian police launched more raids in Brussels and beyond early Monday, detaining five more people as they continued their hunt for a fugitive suspect in the Paris attacks.

In Paris, British Prime Minister David Cameron said he will ask for parliamentary approval for the U.K. to join airstrikes against Islamic State extremists in Syria.

The raids began late Sunday, capping a tense weekend that saw hundreds of troops patrolling and authorities hunting for one or more suspected extremists including Salah Abdeslam, a fugitive since being named a suspect in the Nov. 13 Paris attacks. Between Sunday night and midday Monday, 21 people were detained

The Belgian government kept the capital on the highest state of alert in the face of what it described as a “serious and imminent” threat, preventing a return to normal in the city that is also host to the European Union’s main institutions.

Federal prosecutor Eric Van Der Sypt said 19 raids were carried out Sunday in Molenbeek, home to many of the Paris attackers, and other boroughs of Brussels, and three raids were carried out in Charleroi. Abdeslam was not among those arrested. Van Der Sypt said no firearms or explosives were found.