Madonna has allegedly refused to co-operate with officials investigating the collapse of her stage which killed two men.

The '4 Minutes' singer has reportedly "declined" requests to be interviewed as the probe into the tragedy is launched.

Briton Charles Prow, 23, and Frenchman Charles Criscenzo, 53, were killed when the partially-built roof for the set caved in, bringing down a crane as it was being built at Marseille's Velodrome stadium. Five other crew members were seriously injured.

Magistrates say the 50-year-old star is an important witness as she has a ￡60 million contract with concert promoters Live Nation, the company organising the show.

Madonna, who is currently on the European leg of her 'Sticky and Sweet' world tour, paid tribute to all the workers, saying: "I'm devastated at the tragic news. My prayers go to those who were injured and their families."

The 50-year-old pop star was told of the death while she was rehearsing for her concert at Friuli Stadium, in Udine, Italy, last Thursday (16.07.09).

Later in the evening, she stopped her performance and tearfully told the audience: "I ask you for a moment to stop and think of the people who have lost their lives, we need to appreciate life, the people we love and our families."