Paris officer stabbed as three arrested over Notre Dame plot

French police arrested three women on Thursday in connection with a car packed with gas canisters that was found parked near Paris's Notre Dame cathedral, officials said.

The women, ages 39, 33 and 19, were arrested in Boissy Saint Antoine in the Essonne region, southwest of Paris, French Interior Minister Bernard Cazeneuve said at a news conference. He said they appeared to be preparing "new violent and imminent actions," according to NBC News.

One of the women was a daughter of the car owner, a source close to the investigation said, adding that a police officer was stabbed during the arrest. Other police opened fire and wounded the woman.

Four people - two brothers and their girlfriends - were already in custody over the gas canisters.

A 34-year-old man and a 29-year-old woman, the first couple arrested, have been held since Tuesday and are known to the security services for links to radical Islamists.

The man's brother and his girlfriend, both aged 26, were arrested late Wednesday, the source said.

On Wednesday, French police announced they were holding a couple with links to militants after cylinders were found in the car, sources close to the investigation said.

The Peugeot 607 was discovered abandoned with its headlights flashing at the weekend in a part of the city that is hugely popular with tourists, the sources said.

Anti-terror investigators have launched a probe, and the man and woman, both known to security services, were arrested on Tuesday on a motorway in southern France.

The car's owner, known to authorities for his Islamist preaching, was released on Tuesday evening.

France remains on high alert after a string of attacks, including last November's coordinated Islamic State (IS) group assaults in Paris by gunmen and suicide bombers who killed 130 people.

Florence Berthout, the mayor of the district where the vehicle was found, complained in a letter to the Paris police chief that the car was "illegally parked for more than two hours, despite several telephone calls to police headquarters".

The comment comes after authorities faced heavy criticism for security lapses in July, when 86 people were killed by an Algerian national ploughing a truck into a crowd celebrating Bastille Day in the resort of Nice.

The Islamic State group said the driver, Mohamed Lahouaiej Bouhlel, was one of its followers.

Less than two weeks later, two young militants murdered a priest near the northern city of Rouen.

Interior Minister Bernard Cazeneuve said the latest arrests come at a time of heightened vigilance for potential attacks, adding that "the intentions of those arrested" were as yet unknown.

Notre Dame, renowned for its flying buttresses, stained-glass windows and gargoyles, is one of Paris's most popular landmarks, attracting 13 million visitors each year.

The head of France's DGSI domestic intelligence service, Patrick Calvar, warned in May of a "new form of attack" in which explosive devices would be left near sites that attract large crowds.

Such attacks would create large numbers of victims without sacrificing suicide bombers, he told a parliamentary committee.

French security services are particularly worried about the danger posed by militants returning from Syria after fighting with IS forces, as 700 French nationals are still in that country, according to the country's top prosecutor.