French Interior Minister Bernard Cazeneuve said on Thursday that three women aged between 19 and 39 were arrested in connection with the discovery of six gas cylinders in the French capital on Sunday.

Cazeneuve said the suspects were "radicalized fanatics" who were preparing "new violent … and imminent actions."

All three were seized together in Boussy-Saint-Antoine, south of Paris, an inquiry source said. A police officer also suffered a knife wound during the arrest, the source added.

Abandoned vehicle

A bar employee working near the Notre Dame first raised the alert on Sunday after noticing a gas cylinder on the back seat of the parked car, police said. The car had no number plates and its hazard lights were flashing.

Although the cylinder on the back seat was empty, five full cylinders were discovered in the trunk of the car. Three bottles of diesel fuel were also discovered in the Peugeot 607, but police found no detonators.

Four other people - two brothers and their girlfriends - were arrested earlier in the week.

The first couple to be arrested - a 34-year-old man and a 29-year-old woman - are known to the security services for links to radical Islamists.

More people are still being sought in the Notre Dame case, the prosecutor's office said.

Fears of more terror attacks

France is on alert after a string of attacks by militants linked to the "Islamic State" (IS) group and threats against key buildings.

In July, close to 90 people were killed when a truck plowed into a Bastille Day crowd in the southern resort of Nice, with IS saying it was driven by one of its followers.

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

Those incidents follow two deadly attacks in Paris last year, which left more than 140 people dead, also claimed by Islamist militant groups.

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.

French security services are particularly worried about the danger posed by extremists returning from Syria after fighting with IS forces. Around 700 French nationals are still in Syria, France's top prosecutor said last week.

ksb/kl (Reuters, AP, AFP)