Crans-Montana, Switzerland - The owner of the bar in a Swiss ski resort town ravaged by a deadly fire during New Year's Eve celebrations insisted to Swiss media Friday that safety norms had been followed.

Jacques Moretti, a Frenchman who manages the Le Constellation bar with his wife Jessica, told the Tribune de Geneve daily that the establishment had faced "three inspections in 10 years".

"Everything was done according to the regulations," he said.

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The question of whether safety standards were respected has raged ever since the devastating blaze erupted in the basement of the bar, killing 40 people and injuring 119, according to the toll given by police Friday.

Le Constellation, located on the ground floor of a residential building, has a capacity of 300 people, plus another 40 people on its terrace, according to the Crans-Montana website.

Several witnesses said the event space in the basement of the establishment, where the fire began, was connected with the ground floor by only a staircase, which some described as "narrow".

The lead prosecutor in Switzerland's southwestern Wallis canton Beatrice Pilloud said safety standards at the bar were among the focuses of the ongoing investigation into the tragedy.

She told reporters Friday that the leading hypothesis was that "sparklers or Bengal candles attached to champagne bottles and lifted too close to the ceiling" had ignited the blaze.

The mini-fireworks, stuck in the top of champagne bottles, were being waved near the basement bar's low ceiling, covered in thin soundproofing foam, according to the images posted to social media.

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One video showed the ceiling catching alight and the flames spreading quickly, with revellers initially continuing to dance, seemingly unaware of the death trap they were caught in.

Pilloud said that the bar managers, reportedly from Corsica and the French Riviera, escaped unharmed and were questioned as witnesses, with no liability established at this stage, she said.

Their information explained the layout of the bar, details about recent renovations, and the bar's capacity, as well as indications to help with filling out a list of people present at the time of the fire, Pilloud said.

"The investigation will determine whether this foam is compliant" or not, she added.

According to media reports, Jacques Moretti was not in the bar when the fire erupted, but was at the other of the couple's two establishments at the time.

Jessica Moretti was there at the time of the disaster, and had suffered minor injuries but had been able to return home.

Her husband told the 20Minutes news site that he and his wife were distraught.

"We cannot sleep or eat," he said.

He stressed that they were fully cooperating with the investigation.

"We will do everything we can to help clarify the causes," he said. "We are doing everything in our power."