Islamic State (Daesh) is made up of 30,000 "monsters," a number low enough to defeat, the French foreign minister said, while the premier spoke in parliament of the threat of a chemical attack.
The militant group claimed responsibility for the attacks in Paris that killed 129 people and injured 352 on Friday. It prompted France to declare all-out war against the militants, with other nations such as Russia offering their support.
"There has been an opening from Russia, we think it is sincere. We need to gather all our forces against Daesh, who are monsters, but there are only 30,000 of them," Foreign Minister Laurent Fabius told France Inter radio, using the Arabic acronym for Islamic State.
The minister said he could not believe that "all the countries of the world cannot defeat 30,000 people," and added: "We know that the battle will be long, but the French government is absolutely determined."
Prime Minister Manuel Valls warned that militants could be ready for anything, including the use of chemical or biological weapons.
"Today, nothing can be excluded," he told the French parliament. "I say this of course with all the caution required, but we know it and we have it in mind. There can also be the risk of chemical or biological weapons."
The legislature was due Thursday to take up a proposal to extend the state of emergency imposed in France after the attacks by three months. A ban on public demonstrations in the region of Paris will be prolonged until Sunday, police announced. Authorities have been keen to prevent large gatherings of people amid fears of a new attack.
A new structure to handle young radicalized people will also be created, Valls said - the latest in a series of measures that the government plans to deploy in response to last week's attacks.
The investigation into those killings continued Thursday, one day after a violent raid in the Paris suburb of Saint-Denis that had been meant to capture Abdelhamid Abaaoud, the 28-year-old Belgian suspected of having masterminded the attacks.
It was still unclear on Thursday whether Abaaoud may be among the people who died in the raid. Authorities expect the identification of the bodies to take time because of their condition following a raid that featured a suicide bombing and 5,000 bullets fired by police.
A manhunt has also been underway since Sunday for Salah Abdeslam, a 26-year-old French resident of Belgium who is suspected of having been part of a commando in the attacks.
Police are additionally searching for a man suspected of having provided explosives and detonators to the attackers, the Belgian newspaper De Standaard reported.
It identified the suspect as Mohamed K, a man originally from the Antilles who lived in the northern French city of Roubaix. The suspect is described as "very dangerous," the newspaper wrote.
French investigators have circulated his picture and Belgian police are involved in the search, De Standaard reported, although it was unclear if he is in Belgium.
Belgian law enforcement on Thursday carried out six raids focusing on people with links to another Paris suicide bomber, Bilal Hadfi. The Belgium resident was identified as one of the assailants who blew themselves up near the Stade de France football stadium.
Prosecution spokesman Eric Van Der Sypt told the Belga news agency that the raids were not directly connected to the Paris attacks, stemming instead from an investigation launched earlier this year after Hadfi left Syria.
Another raid was also carried out on Thursday morning in the Brussels suburb of Laken. This operation was connected to the Paris attacks, Belga wrote. One person was detained, RTBF reported.
By Alexandra Mayer-Hohdahl and Alvise Armellini
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