Four rhinoceros heads have been stolen from a storage facility at the National Museum of Ireland, likely for the illegal trade of powdered horn that is used in traditional Far East medicine.

A security guard was tied up by a number of raiders in the 17 April incident, at the Dublin museum.

A total of eight horns have been taken, which could have a street value in the region of 500,000 euro (US$651,153, £427,382).

Rhino horn is now worth more than its weight in gold and in 2011 more than 50 thefts were reported from European museums, galleries and auction houses.

While rhinos have long been targeted in the wild for their horns, in recent years thieves have turned to museums and private collections that include rhino taxidermy and artworks that include rhino horn.

The National Museum of Ireland removed all rhino horns from display over a year ago as a result and placed them in storage.

Earlier this month scientists at Science and Advice for Scottish Agriculture (SASA) announced they were compiling a DNA database of rhinos in museums and zoos across the UK.

The DEFRA-funded project, which may expand to include European specimens if funding is found, will help police investigations into rhino horn theft.