LONDON (AP) ― Fake rhino horns, anyone? That’s all thieves who broke into a British museum have to show after a misguided robbery early Saturday.

The thieves were seeking valuable rhino horns that can be sold in illicit markets for their purported aphrodisiac and medicinal use, but they left with worthless replicas instead.

Officials at the Natural History Museum at Tring had replaced the real horns with replicas because of a recent surge in rhino horn thefts at museums, galleries and auction houses throughout Britain and continental Europe.

Police believe organized crime gangs using mainly smash-and-grab techniques are behind the rash of rhino horn thefts.

“We have been made aware of approximately 20 thefts of rhino horn from museums and auctions houses across the UK and Europe in the past six months,” said Ian Lawson, a Metropolitan Police detective specializing in arts and antiques.

“Additionally we have been made aware of incidents in the UK where premises that have rhino horn on display have been subject to hostile reconnaissance,” he said, advising museums to consider removing authentic rhino horns from public view.

Rising demand for the horns and a crackdown on the illegal trade of them have made rhino horns extremely valuable. U.K. officials say the real horns sought by the thieves Saturday would have been worth about 240,000 pounds ($391,000) on the open market.

The horns are now twice as valuable as gold, police said. They are often used in powdered form by Asians or other people who believe they can cure serious diseases or boost sexual performance, claims that are strongly denied by rhino conservation activists.

Nothing else was taken from the Natural History Museum at Tring during the break-in between 4 a.m. and 5 a.m. Saturday. The thieves apparently used a large hammer to remove the bogus horns from the two rhinos’ heads.

The museum, located 48 kilometers northwest of London in the county of Hertfordshire, was closed Saturday while police investigated and museum workers repaired display cases. It planned to reopen Sunday.

A museum spokeswoman who asked not to be identified because of security concerns said the replicas, made of resin, were put in place three months ago as a precaution.

“Just looking at the quantity and spread of thefts since February shows that this is a real and serious threat to museums with rhino horns,” she said.