Three women arrested in connection with a car loaded with gas cylinders found in a side road near Notre Dame cathedral had been planning an attack on a Paris railway station, the French interior ministry said.

“An alert has been issued to all stations but they had planned to attack the Gare de Lyon on Thursday,” a ministry official said on Friday after the arrests overnight.

The Gare de Lyon station is in the southeast of the capital, less than 3 kilometres from the cathedral which marks the centre.

The official also said the youngest of the three women, a 19 year-old whose father was the owner of the car and who was already suspected by police of wanting to go and fight for Islamic State in Syria, had written a letter pledging allegiance to the militant Islamist group.

The discovery on Saturday night of the Peugeot 607 laden with seven gas cylinders, six of them full, triggered a terrorism investigation and revived fears about further attacks in a country where Islamist militants have killed more than 230 people since January, 2015.

Scores of religiously radicalised people of French and other nationalities are in Syria and Iraq fighting for Islamic State. Many of those involved in recent attacks in France have either taken part in the fighting or had plans to.

France is among the countries bombing Islamic State strongholds, and the group has urged supporters to launch more attacks on French soil.

One of the women stabbed a police officer during her arrest before being shot and wounded, Interior Minister Bernard Cazeneuve said late on Thursday. Other officials said it was the teenager who attacked the officer.

TV footage showed a policeman leaving the scene of the arrests on the outskirts of Paris carrying a large knife.

Police sources said no detonator had been found in the car, though the vehicle also contained three jerry cans of diesel fuel.

When it was found in the early hours of Sunday morning the car had no registration plates and was left with its hazard lights flashing.

“These three women aged 39, 23 and 19 had been radicalised, were fanatics and were in all likelihood preparing an imminent, violent act,” Cazeneuve said in a televised statement. They bring to seven the number of people detained since Tuesday.

The arrests took place in Boussy-Saint-Antoine, some 30 km (20 miles) south-east of Paris.

The car’s owner was taken into custody earlier this week but later released. He had gone to police on Sunday to report that his daughter had disappeared with his car, officials said.

A car, whose owner is on an intelligence services watchlist of people suspected of religious radicalisation, was discovered near Notre-Dame cathedral in Paris on Saturday night with seven gas cylinders inside, police and judicial officials said on Wednesday.

The car owner was taken into custody but later released, one judicial official said. A couple, aged 34 and 29, were arrested at a motorway lay-by on Tuesday in southern France in connection with the incident and remained in custody, the official said.

The Peugeot 607, which had no registration plates, contained seven gas cylinders, one of them empty on the front passenger seat, two police officials said.

It was found with its hazard lights flashing, as if to attract attention, they said.

Interior Minister Bernard Cazeneuve said he was waiting for a report from investigators on what the possible motives were for the incident.

There was no detonating device present in the car, found on a Seine riverside stretch called the Quai de Montebello, metres from the Notre-Dame cathedral, one of Paris’s many popular tourist attractions.

Documents with writing in Arabic were also found in the car.

More than 200 people have been killed in terror attacks over the past year-and-a-half in France.

France remains on maximum alert after calls by the Islamic State group for followers to attack the country, which is bombing the militant group’s bases in Iraq and Syria.

Florence Berthout, mayor of Paris’s Fifth Arrondissement (District), said the incident highlighted the need to beef up security and put more police on patrol in one of the world’s most visited cities.

She said the vehicle was left in a zone where parking is strictly prohibited and that it had remained there for around two hours before it came to the attention of police.

“Police and army staffing must be stepped up,” she told news TV channel BFM.

Thousands of extra police and soldiers have been deployed to patrol sensitive sites across France since 130 people were killed by Islamist gunmen and suicide bombers in multiple attacks on Paris last Nov 13.

A state of emergency declared at that time is still in place and gives police extra search and arrest powers but debate still rages over security levels, following a further attack on July 14 in which a man mowed into crowds in the city of Nice, killing 86.