The United Nations allowed a special relaxation of its international trade ban on condition that tusks from Namibia, Zimbabwe and Botswana were harvested only from elephants that had died of natural causes or killed to control population.

All proceeds from the deal, under which Japan imported 50 tonnes of ivory, must go towards elephant conservation.

Southern African countries have huge stockpiles of ivory

"We are completely satisfied that all the conditions were met," said Mario Hernandez, a member of the UN team which supervised the unloading of the ivory at a Tokyo harbour.

The chairman of the Japan Ivory Association, Kageo Takaichi, said the imports would contribute both to the conservation of elephants as well as to the maintenance of Japanese culture.

Ivory is an important part of Japanese life and art, and is used to sculpt figures and make seals for use on official documents.

Concerns over hunting

However, environmental groups say they are worried that, if such trade is sanctioned, it could lead to an upsurge in elephant hunting.

The World Wildlife Fund said it would continue to monitor the traffic in ivory.

The amount Japan has paid for the ivory has been kept secret until later this year under the terms of the contract between Japan and the exporting countries.

The ivory was sold in a series of auctions earlier this year - but Japan was the only country allowed to bid.

The UN said the sale had been limited to one country in order to ensure that higher demand did not encourage elephant hunters.

Trampling crops

In the 1980s, Japan was the biggest purchaser of ivory in the world. In that decade, the population of the African elephant dropped by half.

Zimbabwe, Namibia and Botswana - known as the ZNB group - argue their herds of African elephants are now so large they are damaging the environment.

They say the elephants trample crops and destroy the vegetation on which other animal species depend.

In other African countries, elephant numbers have yet to recover from the poaching of the 1970s and 1980s.

Kenya has been one of the biggest supporters of the ban. It lost 85% of its elephants to poaching between 1973 and 1987.