Rhino horn thieves in Britain have been foiled by staff who had replaced the £240,000 rare specimens with replicas.
The models were put in place three months ago following a string of similar raids across Britain and Europe.
But while real horn is worth around £50,000 a kilo, the fakes stolen from the Natural History Museum at Tring, in Hertfordshire, have no financial value.
Museum staff believe they were targeted by the same gang that has preyed on auction rooms, galleries and private collections in recent months.
Last month, an Irish crime gang was identified as a significant player in the theft and illegal trade of rhino horn.
In a statement, Europol said it had identified an 'Irish and ethnically-Irish' organised criminal group who had used intimidation and violence to obtain and sell the rhino horn.
Paul Kitching, manager of the Natural History Museum at Tring, said: ‘We're deeply saddened by this pointless theft. The rhinoceros horns that have been stolen were replicas made out of resin, so they have no commercial value.
‘We're now working with the police and urge anyone with any pertinent information to get in touch. We are working today to clear up the museum so that we can re-open as usual tomorrow.’
The two stolen replicas were taken from an Indian and a white rhino. Both weigh around 2kg.
Nothing else was taken during the break-in which comes just a week after Britain secured international agreement to clamp down on the illegal rhino horn trade.
The horn itself has now become so sought after it is worth more than diamonds, gold, heroin and cocaine.
UK officials have warned that its sale is being driven in part by a belief that it can cure cancer or reverse the effects of stroke.
In Asia, it is often powdered and used for medicinal purposes.
Countries and conservation groups across the world are now working together by sharing intelligence, policing tactics and public awareness campaigns to end the trade amid fears it could stimulate poaching.
Hertfordshire Police said officers are investigating the museum theft.
The thieves smashed through the museum's front doors between 4am and 5am this morning, a spokesman said.
It is believed they removed the horns from the animals using a large hammer.
