An employee of a nearby bar flagged the car on Sunday morning as it was parked along the Seine River with its hazard lights flashing, according to two French officials. No one was inside, but police found six cylinders filled with gas in the trunk and an empty cylinder on one of the seats.

The officials said the car's owner and another person were taken into custody.

French Interior Minister Bernard Cazeneuve said it still was not clear why the car was abandoned or what the intentions were of those under arrest.

Mr Cazeneuve said there have been 260 arrests linked to extremist networks since the beginning of the year "and a significant number of these people were preparing attacks".

No detonator or ignition materials were found in the car, the officials said.

France is on alert after a deadly string of Islamic State group attacks and threats against landmarks. News of discovery broke hours before the release of a government-commissioned report on how the attacks have impacted France's lucrative tourism industry.

Algeria-linked extremists used gas canisters filled with nails during attacks on Paris in the 1990s.