A London diamonds show that included the Millennium Star and a gem-encrusted dress has been closed more than three months early after police warned of a planned robbery.

The exhibition opened July 8 at the Natural History Museum in west London's Kensington district and was to run until Feb. 26. It closed yesterday to ensure the safety of visitors and workers, the museum and Steinmetz, the main sponsor of the show, said in statements.

Police altered their advice on the show's security two days ago, with a warning that "indicated a heightened criminal risk to the exhibition," museum Director Michael Dixon said in a statement on the institution's Web site.

In addition to the 203.04-carat De Beers Millennium Star, the world's largest flawless, colorless diamond, the show included the 59.6-carat Steinmetz Pink, the biggest flawless fancy vivid pink stone, and a dress encrusted with 3,000 diamonds. The garment, worth 5 million pounds ($8.6 million), was worn by Irish singer Samantha Mumba at the London premiere of the film "Spider-Man 2."

The hundreds of stones on display can't be valued, museum spokeswoman Becky Chetley said in a telephone interview.

"We haven't put a value on the show because most of the pieces are literally priceless," Chetley said. "We were obviously aware of the risk because diamonds have an incredible commercial value."

The Millennium Star and 11 other diamonds were the target of a robbery attempt during a show at London's Millennium Dome in 2000, the only other occasion the stone had been exhibited in the U.K. The pear-shaped Millennium Star was unveiled at the site in 1999. Police arrested 11 men after a gang used a bulldozer to smash into the dome. Police acted on intelligence and switched the gems with replicas before the raid.

This time, police advised the Natural History Museum to shut the exhibition before any attempt could be made.

"We have received information that leads us to believe that criminals were planning to target this exhibition, and for the safety of staff, visitors and exhibition specimens, we have advised the management to close the exhibition with immediate effect," London police said in a statement.

Steinmetz, a company in Geneva that mines, polishes and cuts diamonds, said in an e-mailed statement that police advised it of "a robbery attempt anticipated to occur later this week." No further details were available.

The Diamond Trading Co., a London-based unit of De Beers, the world's biggest diamond company, also sponsored the show.

Actress Sophie Marceau in 1999 with the Millennium Star.