LONDON -- The organisers of Michael Jackson's 50 comeback tour dates in London remained guarded Saturday about refunds for ticket holders following the singer's death.

Jackson fans from around the world had rushed to snap up tickets for the 'This Is It' performances at London's O2 Arena which were due to start on July 13.

The reclusive star made his final public appearance to unveil the sellout gigs in March.

Reports in Britain say about 50 million pounds (59 million euros, 83 million dollars) has been spent on 750,000 tickets.

Promoters AEG Live made no comment immediately following Jackson's death, but a spokeswoman for the company said late Friday:

"On behalf of the entire AEG organisation we extend our deepest condolences to Michael Jackson's family and friends during this tragic time."

Full ticket refund information and procedures will be released early next week for all Michael Jackson 'This Is It' shows.

"Fans are advised to hold on to their ticket vouchers/proof of purchase."

Most tickets for the concerts cost between 50 pounds and 75 pounds. While fans who bought from official outlets are likely to be reimbursed, those who obtained tickets from other sources could lose out.

Tony Northcott, a spokesman for British consumer body the Trading Standards Institute, said: "Sales coming through a third party like eBay or a man in the pub will be on sticky ground.

"If sales are through a third party, then the terms and conditions disappear."

Trading website eBay, where tickets had fetched prices of up to 1,300 pounds, has urged customers to contact the individual sellers to discuss a refund.

The Times newspaper reported Saturday that AEG had hoped to recoup much of the estimated 10 million pounds it would have cost to stage the concerts from merchandising and corporate entertainment.

With that possibility now quashed, question marks also remain over the extent of AEG's liability for the Jackson concerts.

Quoting industry sources, the Times said insurers could face a bill of around 50 million pounds, but that was expected to be a fraction of the cost to AEG of cancelling the 50 dates and leaving the O2 venue empty for months.

Most estimates put the figure at 300 million pounds.

The president of AEG Live, Randy Phillips, had said the company was insured for "the first 23 days" of the run and negotiations were ongoing to increase that.

Concerns for Jackson's health rose when the start of the shows was pushed back after the initial announcement.

But Phillips had insisted the rescheduling was due to the "sheer magnitude" of the show and insisted at the time: "I would trade my body for his tomorrow. He's in fantastic shape."