Russia's space officials on Thursday rushed to find a replacement for British singer Sarah Brightman after she pulled out as the next space tourist four months ahead of her planned trip.

The singer known for roles in West End musicals such as "Phantom of the Opera" said Wednesday she was suspending her plans to fly to the International Space Station for "family reasons", reportedly her mother's poor health.

In a brief statement, the Russian space agency said it "hopes that all will be well with Brightman's loved ones."

Brightman, 54, had paid $52 million (48 million euros) to fly to the ISS, and hoped to become the first soprano to sing on board. She underwent training and passed health checks.

Speculation in Russia centred on whether Brightman pulled out because of safety fears after an unmanned supply ship to the ISS lost contact with mission control after its launch last month and fell back to Earth.

Brightman wanted to fly "on condition of complete safety -- she didn't want to risk a hair," Igor Marinin, editor of Space News magazine, told RIA Novosti news agency.

Astronauts on the ISS are spending an extra month aboard while Russia investigates the accident.

The next space launch has also been delayed although this was not expected to affect the September 1 flight.

Reports also questioned whether Brightman had failed to raise funds.

The Izvestia daily cited an "informed source" as saying: "As far as we know from our partners, the main reason is that the singer could not attract a big enough sum from sponsors to cover her ISS trip."

The singer,who won a multi-million divorce settlement from composer Andrew Lloyd Webber, has said she is paying for the trip herself.

- Cargo replacement? -

Brightman's place in the spaceship to the ISS may simply be filled with cargo which is needed after the supply ship failure, said Russian space official Sergei Krikalev, speaking to Interfax, calling this the "simplest and quickest solution."

Rumours had circulated for months that the singer might pull out of the 10-day trip. In January she delayed the start of her training to visit her sick mother.

"Several candidates are now being looked at to replace Sarah Brightman," a source in the space industry told Interfax news agency.

"The chances of finding a suitable candidate are small, especially since there's practically no time left for training."

Space Adventures, the US company which books space tourists, "has a few days or a week to find another tourist," another space industry source told TASS news agency.

"Otherwise they'll send a young Russian first-time cosmonaut."

It was unclear whether a Japanese businessman who has been training with Brightman could step in.

The businessman, Satoshi Takamatsu, signed a contract to undergo training, not a far more costly ticket to the ISS, a space industry source told Interfax.

There was no comment on whether Brightman would make another bid to fly to the ISS.

Previous space tourists visiting the ISS on a total of eight trips have included the Canadian founder of the Cirque du Soleil, Guy Laliberte, and Iranian-American entrepreneur Anousheh Ansari, so far the only woman.

Several other space tourists have been rejected in the past for health reasons or failed to come up with the money.

Russia in 2002 rejected then-22-year-old US singer Lance Bass from boyband NSYNC for failing to pay for his training.