The local authorities failed to carry out yearly safety inspections between 2020 and 2025 at the bar in the Swiss Alps that suffered a deadly fire last week, Swiss officials acknowledged on Tuesday, amid mounting accusations that lax oversight had set the stage for the disaster.

“We bitterly regret this,” said Nicolas Féraud, the mayor of Crans-Montana, the ski resort town where the fire killed 40 people, many of them teenagers, and injured over 100 others during New Year’s celebrations.

Speaking at a news conference, Mr. Féraud said that “the justice system will determine the extent to which this failure influenced the chain of events leading to the tragedy.” Local fire regulations mandate yearly inspections in buildings that are open to the public or present special risks.

But Mr. Féraud said that as of May 2019, when the last inspection took place, security inspectors had flagged no major issues with the bar, Le Constellation, and that its owners had addressed minor ones, like installing an “anti-panic handle” on a door. Inspections were also done in 2016 and 2018, he said.

“We never received any alerts,” Mr. Féraud said.

The owners, a French couple named Jacques and Jessica Moretti, are under criminal investigation over suspicions that negligence played a role in the fire — a sudden burst of flames that engulfed the bar’s basement.

The Morettis have not responded to multiple requests for comment. In brief interviews with the Swiss media, they have denied wrongdoing and said they were cooperating with investigators.

The local authorities have also come under pressure over their enforcement of fire safety regulations.

Pictures on social media of extensive renovations when the bar opened in 2015, as well as witness accounts of its operations, suggest that hazards blamed for turning the bar into a death trap were long present.

Those include a basement ceiling covered in flammable foam, the indoor use of firework sparklers and a lack of accessible emergency exits that turned a narrow staircase into a choke point.

Swiss investigators believe that sparklers used in the basement caused the fire. Witnesses and videos suggest that the fireworks were placed on bottles of alcohol, sending up sparks that ignited foam insulation covering parts of the ceiling.

Mr. Féraud, the mayor, said on Tuesday that Crans-Montana had decided to ban the use of pyrotechnic devices indoors and to commission an external firm to “immediately” inspect public establishments.

Le Constellation, a town popular with wealthy tourists, was an affordable option for young people. The legal drinking age in Switzerland is 16 for beer and wine and 18 for high-proof alcohol, although local rules prohibit minors aged 16 or less from bars after 10 p.m. unless they are accompanied by an adult.

On Monday, the Swiss broadcaster RTS published a video that it said had been filmed by a patron during New Year’s celebrations at Le Constellation in 2019. Someone in the video says, “Watch out for the foam!” as the sparklers are hoisted toward the ceiling.

Mr. Féraud said that local officials had not been aware of the video, which he said showed the bar manager’s “negligence.”

But he denied that the local authorities were trying to evade responsibility. He fended off calls for his resignation, saying he trusted Swiss courts to establish the truth about the fire.

Peppered by questions in French, Italian and German, Mr. Féraud said he could not explain the lack of inspections, a failing that he said came to light after the municipality dug into its archives last week and handed over documents to investigators.

Before 2020, he insisted, the local authorities had followed the rules.

Mr. Féraud said that the soundproofing foam on the ceiling of the bar’s basement had never been flagged as a hazard, because fire regulations do not make local safety inspectors responsible for checking building materials. It is unclear whether regional or federal Swiss authorities would have been responsible for doing so.

While the authorities in Crans-Montana insist that giving documents to investigators was an act of transparency, some criticized the move as an attempt to pre-empt potential liability.

Sébastien Fanti, a lawyer for three Swiss citizens injured in the fire, said that it was unusual for authorities who might face criminal responsibility to “bring you the proof of their work.”

“When 40 people are dead, you carry out a raid” to seize documents, he said. “You do the work that any other police force in any other country would have done.”

The local authorities, he added, “are trying to save their skin and to say they did everything right.”

Some have also questioned a decision by prosecutors to let the Morettis go free during the investigation, on the grounds that they were not a flight risk.

In Italy, where the bodies of five victims were flown back this week, Matteo Salvini, the infrastructure and transport minister, faulted “those who failed to ensure safety in that basement, those who failed to check, those who gave permission.”

“In civilized Switzerland, prison doors will have to open for several people,” he wrote on social media.

Elisabetta Povoledo contributed reporting from Rome.