French PM Manuel Valls has warned that France could face chemical or biological attack from terror groups, as MPs debate extending the state of emergency after the Paris attacks.
Belgian police are meanwhile raiding six properties in and around Brussels, linked to suspected Paris attackers Bilal Hadfi and Salah Abdeslam.
It remains unclear whether the suspected organiser of the attacks was killed in Wednesday's raid in Paris.
Friday's attacks killed 129 people.
Valls was addressing the French parliament ahead of a vote to extend the state of emergency by three months.
He told MPs that "terrorism hit France, not because of what it is doing in Iraq and Syria ... but for what it is".
"What is new are the ways of operating; the ways of attacking and killing are evolving all the time," the prime minister said.
"The macabre imagination of those giving the orders is unlimited. Assault rifles, beheadings, suicide bombers, knives or all of these at once."
Valls also called for Europe to adopt measures on sharing information about airline passengers as a way of protecting collective security.
French authorities say that they foiled another attack in Wednesday morning's raid on a flat in the northern Paris suburb of Saint Denis.
Eight people were arrested in the raid, in which police fired over 5,000 rounds of ammunition, but those arrested did not include Abdelhamid Abaaoud - who investigators suspect was the ringleader of the attacks.
At least two people were killed in the raid, one of them a woman who blew herself up with a suicide vest.
She is widely reported to be Hasna Aitboulachen, a cousin of Abaaoud.
The Washington Post quoted unnamed European officials as saying Abaaoud, a 27-year-old Belgian, was killed in the raid, but French authorities told AP the identities of the dead remain unclear.
Further attacks by IS were also likely elsewhere in Europe, according to the head of the EU's law enforcement agency Europol.
Rob Wainwright was addressing MEPs in Brussels ahead of an emergency meeting on Friday of EU interior ministers on the Paris attacks.
Most of the Belgian raids are targeting properties in Jette and Molenbeek connected to Bilal Hadfi, a Frenchman living in Belgium who was one of the seven attackers killed in Paris, Belgian broadcaster RTBF reports.
A further raid, at an address in the Brussels district of Laeken, is linked to Salah Abdeslam - a suspected attacker who is believed to be on the run - Belgian authorities told the BBC.
However, the raids had been planned for some time and were not part of the manhunt, the prosecutor's office told Belgian media.
Following Friday's attacks on a concert hall, cafes and the Stade de France stadium, President Francois Hollande declared a state of emergency for 12 days.
The bill going before France's lower house of parliament on Thursday and the senate on Friday includes:
--Extending the state of emergency for three months
--Placing under house arrest anyone deemed to be a public threat
--Barring suspects from communicating with each other
--Allowing police to carry out searches at any time, without the prior approval of a judge, if the public is thought to be in danger
Meanwhile the Belgian Prime Minister Charles Michel has announced an extra €400m (£280m) of funding for anti-terror measures following the Paris attacks.
He told the Belgian parliament that he did not accept criticisms of Belgium's security services ahead of the Paris attacks, which France has said were prepared in Belgium.
IS said it had carried out the attacks in response to France's air campaign against its positions in Syria, and pledged further bloodshed.
France has since stepped up its air strikes against IS targets in Syria.
Both France and Russia - which is also targeting militants in Syria - are putting together draft resolutions at the UN Security Council that would lay out an international approach to defeating IS.
President Hollande has urged the council to approve a resolution on fighting IS quickly.