Ammunition seized and at least nine people held in raids in Toulouse and Lyon among other places.
Specialised counterterrorism units have carried out more than 150 raids in eight cities across France and arrested at least nine people in connection with the deadly Paris attack.
Monday’s early-morning raids took place in Toulouse, Paris, Jeumont and Grenoble where police blocked streets and searched houses looking for suspects involved in Friday’s attacks, which killed at least 129 people and wounded hundreds more.
Local media reported 13 raids in Lyon where police said a rocket launcher, among other ammunition, was seized and arrests made.
Al Jazeera’s David Chater, reporting from Paris, said about 200 members of police tactical units surrounded an address in Toulouse and ammunition and a large amount of cash were found at one of the locations.
He said 20 police vans were used in the raid in Jeumont on the French-Belgian border where a house was searched.
Manuel Valls, the French prime minister, confirmed that the raids were linked to Friday’s events and warned that more attacks were being planned.
“We know that operations were being prepared and are still being prepared, not only against France but other European countries too,” Valls told RTL radio.
He added that France was “making use of the legal framework of the state of emergency to question people who are part of the radical jihadist movement … and all those who advocate hate of the republic”.
Earlier, reports emerged that a fugitive directly involved in the attacks was questioned and let go by police near the Belgian border.
French police had released a photo of Brussels-born Salah Abdeslam, 26, who is on the run.
He was suspected of renting the car that delivered attackers to the Bataclan concert hall where more than 80 people were killed.
Abdeslam is thought to be directly involved in Friday’s attacks, French security officials told the Associated Press news agency.
He is one of three brothers believed to be involved in the killings; one was arrested in Belgium and another died in the attack, one official said.
The arrested brother was released, with his lawyer telling Associated Press that her client “hadn’t made the same life choice”.
Abdeslam is also under an international arrest warrant issued by Belgium.
Al Jazeera’s Paul Brennan, reporting from Brussels, said that Belgium had been put on a level-3 alert.
Earlier, security officials had indicated that there was an ongoing search operation in the Belgian capital for Abdeslam and other suspects.
Stepping up their hunt for information, authorities found several AK-47 assault rifles in the back of an abandoned SEAT car in an eastern suburb of Paris.
Witnesses said the car, found in Montreuil, was used by the attackers at multiple locations on Friday night, the AFP news agency reported.
French police had earlier identified Omar Ismail Mostefai, a 29-year-old Paris native, as one of the attackers.
Mostefai’s detached finger was found overnight at the Bataclan concert hall, the scene of the bloodiest attack.
The French citizen had been known to police for his alleged links to armed groups but had not been previously linked to violent activities.
Police are also holding six of the man’s relatives.
French authorities believe the attacks were planned abroad by ISIL, but have not yet confirmed the identities of others involved.
Belgian authorities, however, said that two of the attackers who died were Frenchmen who had lived in Brussels.
In Belgium, police said they have arrested seven people over their alleged links to the attacks and investigators have found that two cars used in the operation were rented in Belgium, they said.
ISIL purportedly claimed responsibility for the attacks shortly after the incident but has not revealed the identities of the attackers.
Greek authorities have confirmed that the holder of a Syrian passport found near the body of an armed man who died in the attacks had registered as a refugee on the island of Leros in October.
Greece identified the man as 25-year-old Ahmad Almohammad, from the northwestern Syrian city of Idlib.
The attacks have intensified debate on Europe’s response to the refugee crisis. Marie Le Pen, the leader of France’s far-right National Front party, has called for a tightening of the country’s borders.
Source: Al Jazeera