The company in charge of scaffolding at Notre Dame Cathedral before the fire admitted Wednesday that some of its staff had smoked on site, but said that was not the cause of the blaze.
Satirical and investigative newspaper Le Canard Enchaine reported earlier that staff had admitted to police that they had breached a smoking ban.
“I can confirm, that’s what they said to the police,” a spokesman for scaffolding and roofing firm Le Bras Freres told dpa. “So we regret that they breached the smoking ban, but it’s a fact.”
“We don’t think that a cigarette butt set Notre Dame on fire,” added the spokesman, who asked not to be quoted by name.
According to Le Canard Enchaine, investigators think a short-circuit most likely caused the fire that destroyed the cathedral’s roof and spire.
The fire had started inside rather than outside the building, and an hour after the workers left, the spokesman for Le Bras Freres argued.
The company was now engaged in emergency works on the cathedral, the spokesman said.
A temporary tarpaulin covering to protect the damaged stone ceiling vaults was likely to be fully in place Wednesday evening or Thursday, he said.
Professional mountaineers have also been called in to help put the tarpaulin in place.
The Culture Ministry meanwhile said that the stained glass windows in the upper storeys of the cathedral would be removed starting from Friday.
Stained-glass windows, through which coloured light streams into the interior of the cathedral, are a hallmark of Gothic architecture.
Those being taken down in Notre Dame, though, date from the mid-20th century.
The mediaeval originals were removed in the 18th century, when they were seen as outdated, and replaced with plain glass. That was in turn replaced in the 19th, and again in the 20th, centuries.
The great rose windows in the west, north and south facades, which have retained their mediaeval glass, are not going to be taken down for the moment, a ministry spokesman told dpa.
The French government meanwhile approved a draft law on the restoration of the cathedral, which will set up a national donation drive promised by President Emmanuel Macron.
Donations will go to the restoration project as well as to training craft workers needed for it, government spokeswomen Sibeth Ndiaye said.
The law, if approved by parliament, would also allow the government to give itself exemptions from existing laws in order to complete the restoration project.
Macron has said he wants the restoration finished in five years, although some experts have cast doubt on how realistic that deadline is.
He has also suggested replacing the 19th-century spire that was destroyed in the blaze with a work of modern architecture.