Paris: A 19-year-old woman arrested in a probe into a car found laden with gas cylinders near Notre-Dame Cathedral had pledged allegiance to the Islamic State group and was preparing an imminent attack, officials said Friday.
French President Francois Hollande said a terror cell had been shut down and an attack "foiled," after Ines Madani, 19, and two other women were arrested.
Police shot and wounded Madani as they swooped on her and her accomplices aged 23 and 39 in a suburb south of Paris on Thursday.
Investigators believe Madani is the main suspect in a probe into the Peugeot 607 found a few hundred metres (yards) from Notre Dame cathedral on Sunday.
She is the daughter of the car's owner.
Interior Minister Bernard Cazeneuve said the three women "were apparently preparing new, violent and, what is more, imminent actions".
The women were "radicalised and fanaticised", he said.
Madani had sworn allegiance to the Islamic State group in a letter found in her possession, according to a source in the investigation.
A police officer suffered a knife wound to the stomach during the arrests late Thursday in Boussy-Saint-Antoine, south of Paris.
Hollande, speaking on a visit to Athens, said: "An attack has been foiled."
"A group has been destroyed," he said, but he warned: "There are others."
A police source said security services had issued a warning Thursday about a possible attack on train stations in Paris and the area where the women lived.
Police are now convinced that the car found with five full gas cylinders in its boot was intended to be used in an attack.
The car was discovered with its hazard lights flashing and its licence plates had been removed.
Three bottles of diesel fuel were also discovered in the vehicle, but police did not find any detonators.
Police said the boyfriend of one of the three women was arrested on Thursday.
The man's brother is himself in custody over suspected links to Larossi Abballa, a jihadist who killed a police officer and his girlfriend in a Paris suburb in June, a source said.
Four people – two brothers and their girlfriends – are already in custody over the discovery of the car.
The first couple arrested, a 34-year-old man and a 29-year-old woman, have been held since Tuesday and are known to the security services for links to radical Islam.
Police then arrested the man's brother and his girlfriend, both aged 26.
Paris prosecutor Francois Molins will give a news conference on the investigation at 1530 GMT Friday.
France is on high alert after Islamic State called on its followers to attack the country in revenge for air strikes on the group's bases in Syria and Iraq.
ISIS has claimed responsibility for a string of jihadist attacks, including last November's coordinated bloodshed in which gunmen and suicide bombers killed 130 people.
Cazeneuve, the interior minister, on Friday told French daily La Presse that 260 people have been arrested in connection with terrorist networks or operations since the beginning of the year.
A bar employee working near Notre Dame had first raised the alert after noticing a gas cylinder on a seat of the parked Peugeot, police said.
Although that cylinder was empty, five full cylinders were discovered in the boot.
"If it was an attack plot, the method was very strange," a police source said Thursday.
The discovery followed a deadly summer in France in which 86 people were killed when a truck ploughed into a Bastille Day crowd in the southern resort of Nice.
ISIS said the truck was driven by one of its followers.
Less than two weeks later, two young jihadists murdered a priest near the northern city of Rouen.
In May, the head of France's DGSI domestic intelligence service, Patrick Calvar, warned of a "new form of attack" in which explosive devices would be left near sites that attract large crowds.