One person has been detained for questioning. The latest search for suspects came as the French prime minister, Manuel Valls, said an attack using â€œchemical or biological weaponsâ€ in France could not be ruled out, and the Belgian prime minister, Charles Michel, asked Parliament to approve a variety of strict new security measures.
French authorities are also continuing the DNA tests to determine whether the Belgian Abdelhamid Abaaoud, suspected of organising the Paris terrorist attacks was killed in a raid on Wednesday.
Separately, the White House said President Obama would not abandon plans to attend climate change talks in Paris at the end of the month despite the security concerns in the city. The Paris prefecture has extended a ban on protests in the Paris area until Sunday.
At least some of the Belgian raids were being conducted in Molenbeek, the Brussels district that has emerged as a crucial link in the investigation of the attacks in Paris on Friday that left at least 129 people dead.
Molenbeek was the base for Abaaoud, the Belgian who is believed to have organised the attacks, and the Abdeslam brothers: Salah, who is still at large, and Ibrahim, who died after he detonated a suicide bomb at a cafe on Friday.
Abaaoud was the focus of a raid on Wednesday in St.-Denis, a suburb on the northern edge of Paris, that ended with eight people in custody. On Wednesday, the French prosecutor, FranÃ§ois Molins, said only that Mr. Abaaoud was not taken into custody.
The authorities were conducting tests on the remains of at least two bodies that were found after the raid, in which a suicide bomber died after she detonated an explosive vest.
Valls, in a speech at the French National Assembly, where lawmakers were debating a three-month extension of a state of emergency, warned that â€œwe must not rule anything outâ€ when considering the possibility that terrorists might use chemical weapons. Mr. Valls also called for reinforced tracking of movements of people within the European Union and urged European countries to improve the sharing of airline passenger information.