The organisers of the Winter Olympics opening ceremony have refused to deny speculation that the US pop diva Mariah Carey lip-synced her part in the show. Carey took to the stage to sing Domenico Modugno’s Nel Blu, dipinto di Blu in Italian, followed by one of her own songs, Nothing Is Impossible, but many social media users quickly claimed that there were several times where her lip movements were out of time with the music.

When asked directly whether Carey was lip-synching, the director of the show, Maria Laura Iascone, confirmed that there had been a pre-recording – but refused to say whether it had been used or the American had sung live.

“During all the ceremonies, in order to be on the safe side, we always record,” she said. “But this is something that is practised internationally in events with high-level broadcasting.”

However, she insisted she had no complaints with Carey’s performance. “Yesterday’s performance was really extraordinary,” she said, “It was fantastic for everybody and we are all satisfied by the results we had. And the images can prove it to you all, because there was magic.”

Iascone confirmed that Carey had not been paid. “We believe that Mariah Carey was exceptional, as were all our artists,” she added. “She was not paid for participation as this was the condition for the opening ceremony. We were really honoured to have her with us.

“We were extremely happy and satisfied with her performance, as a major talent, who has given us the possibility of representing a very joyful moment. And she also sang an Italian song, which people in the stadium felt deeply about.”

A Milan-Cortina spokesperson later told the Guardian that certain elements of the opening ceremony were pre-recorded “to ensure accurate timing, sound quality and a seamless broadcast”.

“The technical, logistical and organisational complexities of an Olympic ceremony are not comparable to a live performance by a single artist,” they said. “The ceremony involves coordinated choreography between multiple artists, speakers, performers and musicians, all of which must align precisely with a live global broadcast.

“The operation for the Milano Cortina 2026 opening ceremony was significant. It involved more than 1,300 cast and performers over multiple locations, over 500 musicians contributing to the musical score, and more than 700 hours of rehearsals across several host venues.

“For this reason, a different production model is required, in which certain elements of the ceremony are pre-recorded to ensure accurate timing, sound quality and a seamless broadcast.”

The International Olympic Commitee played down the boos for the US vice-president JD Vance in the opening ceremony, preferring instead to note the enthusiastic reception given to the USA team. However, IOC spokesperson Mark Adams said that there had been “very good chemistry” between Vance and IOC president Kirsty Coventry when they sat down to discuss the Los Angeles 2028 Olympics.

“With the next games coming up in Los Angeles we are super happy, very happy that the US administration is so engaged with the games here and going forward,” Adams added. “She was very pleased about the enthusiasm of the vice-president and the whole administration for the Games, which obviously for us is an important thing.”

Meanwhile, Italian police said on Saturday they suspected arsonists had struck rail infrastructure near the northern city of Bologna, triggering major disruptions to train traffic on the first full day of the Games. The fire hit a track switch and severed electrical cables used to detect train speed, causing delays of up to two hours for high-speed, Intercity and regional services at one of Italy’s busiest rail hubs.

The blaze was “presumably deliberate” but had not been claimed, a spokesperson for the police said. Italy’s transport ministry called it an act of “serious sabotage“, adding that it echoed the opening day of the 2024 Summer Olympic Games in Paris, when saboteurs struck France’s high-speed TGV train network, causing travel chaos.

“These actions of unprecedented seriousness do not in any way tarnish Italy’s image in the world, an image that the Games will make even more compelling and positive,” said the transport ministry, which is headed by the deputy prime minister, Matteo Salvini.