Diceros bicornis (Linnaeus 1758), Mounted head of black rhinoceros, East Africa. Photo: Courtesy of Nigel Monaghan: Keeper National Museum of Ireland – Natural History

DUBLIN (AFP).- Masked men stole eight rhino horns from the National Museum of Ireland with a street value of about 500,000 euros ($650,000), officials said Thursday.

The gang of three broke into the museum archives building in Dublin late on Wednesday, tied up a security guard and loaded four rhino heads -- each with two horns --- onto a van, police said.

The guard, who was unhurt, eventually freed himself and raised the alarm, but not before the thieves had made off with their haul.

Rhino horns have become increasingly valuable as a component of traditional medicines in Asia, where they are falsely believed to have powerful healing properties.

Poachers feeding the lucrative market have decimated rhino populations across Africa -- in South Africa, more than 200 of the animals have been killed so far this year.

A spokeswoman for the Irish museum said fears about a possible theft had prompted curators to move the horns from public display last year into storage.

"Their price is based on weight and the total amount stolen could have a street value in the region of 500,000 euros," she said.

Police said they had begun an investigation into the theft, adding: "The crime scene is sealed off for forensic technical examination." © 1994-2013 Agence France-Presse

Ceratotherium simum (Burchell 1817), Mounted head of white rhinoceros, East of Yalu River, Moru District, Mongalla, Upper (White) Nile, Sudan. Gift: Maj. C.W. Spinks. Shot 1914. Rowland Ward mount. Photo: Courtesy of Nigel Monaghan: Keeper National Museum of Ireland – Natural History

DUBLIN.- Four rhinoceros heads were stolen from premises of the National Museum of Ireland late in the evening of Wednesday 17 April 2013. A security guard was overpowered by a number of raiders and tied up but has not been injured. He managed to free himself and notify Gardaí who are investigating the robbery. Photo: Courtesy of Nigel Monaghan: Keeper National Museum of Ireland; Natural History.