Ivory from 400 elephants seized
The Madrid haul is the single biggest ever of carved ivory, Spain's Civil Guard paramilitary force said in a statement on Friday.
Members of the Civil Guard's specialised environmental arm Seprona started an investigation last year after confiscating 110 kg (240 pounds) of elephant hair, some of which had been turned into jewellery.
They subsequently found 3.4 tonnes of raw and worked ivory in a store in Madrid, whose owner had a licence to keep less than 500 kg, and confiscated the 2.9-tonne surplus.
"According to experts' initial estimates, the ivory seized could have come from the sacrifice of more than 400 animals," the statement said.
Trade in ivory has been banned worldwide since 1990 by the Convention on International Trade in Endangered Species, an international agreement to which 166 governments adhere.
The agreement has allowed some one-time sales of ivory by South Africa, Namibia and Botswana, despite opposition from animal rights' activists.
A report by Save the Elephants last year said China was the destination of much of Africa's smuggled ivory.