PARIS: A poorly stubbed-out cigarette or an electrical fault could have started the devastating fire that ripped through Paris' Notre-Dame cathedral in April, French prosecutors said Wednesday, while ruling out any criminal intent.

The statement by prosecutors, which also said an investigation was being opened into possible negligence, was the first official evaluation of the causes of the April 15 fire at the world heritage landmark that shocked France and the world.

But well over two months after the fire, it still offered no concrete conclusions over what caused one of the most catastrophic fires involving a cultural monument in the history of Paris.

French investigators were examining many hypotheses "including a malfunctioning of the electrical system or a fire which started with a badly stubbed-out cigarette", said a statement.

But it said there was no evidence to back up any theory of "a criminal origin" to the fire.

The statement, signed by chief Paris prosector Remy Heitz, said the preliminary conclusions had been based on 100 interviews with witnesses.

But it emphasised that the investigation had still not identified the actual cause of the fire, even if "certain failures" had been laid bare.

It was not yet possible to conclude whether an electrical fault or a cigarette is the most likely theory, it added.

"Deeper investigations, using significant expertise, will now be undertaken," it said.

- Steeple debate -

The statement said a preliminary investigation for negligence had been opened, without targeting any single individual.

The inquiry has been entrusted to three investigating magistrates who have the power to press charges against anyone suspected of negligence.

In April, a spokesman for scaffolding company Le Bras Freres which had been involved in restoration work admitted that workers had smoked on the site from time to time.

"We regret it," the spokesman said at the time, adding: "In no way could a cigarette butt be the cause of the fire at Notre-Dame."

The April 15 inferno felled the steeple and consumed the 12th-century lattice of oak beams supporting the roof. However, to global relief, the two great mediaeval main towers of the edifice survived.

The damage to the beloved landmark, which survived the French Revolution and two World Wars, triggered an international outpouring of emotion and pledges of donations towards its reconstruction.

President Emmanuel Macron has set an ambitious target of five years to restore it.

Up to 150 workers have been working at the cathedral daily since the fire, continuing to remove debris and stabilise the structure.

On June 15, two months after the fire, clerics conducted the first mass inside the cathedral since the blaze, donning hard hats along with their robes for their safety.

Macron has called for an "inventive" rather than identical reconstruction of the 19th-century steeple, but polls show the French favouring a more conservative approach.

A YouGov survey published at the end of April showed that 54 percent want the iconic cathedral to be rebuilt in identical fashion.

Legislation on the reconstruction has been blocked in parliament over disagreements between the upper and lower houses and is now only expected to be adopted at the end of July. —AFP