The Japanese arm of the World Wide Fund for Nature urged Yahoo Japan Corp. on Thursday to impose tighter restrictions on the trade of ivory items on its auction site, saying it serves as a major venue for ivory trade and encourages poaching.

Among other major e-commerce companies in the country, trading of ivory items has disappeared on the site of Rakuten Inc. and sharply declined on Mercari Inc.'s community marketplace app after they banned ivory sales, according to a recent survey by WWF Japan.

[Courtesy of WWF Japan]

The survey conducted between June and July found ivory items worth 37.8 million yen ($340,000) were sold in four weeks on the Yahoo Auctions site, and 88 percent of them were processed ivory with no proof of sellers having legally obtained them.

"A person charged in an ivory smuggling case in China testified during trial to obtaining ivory through (Yahoo Japan's) Yahoo Auctions. It became clear that the site has been used by crime groups," a WWF Japan official said.

Japan remains one of the world's largest ivory markets and is home to an active, though shrinking, ivory industry, according to WWF Japan. A number of countries including the United States and China have closed their domestic markets for ivory.

The Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention, prohibits international trade of ivory in principle to protect African elephants, which are under threat of extinction.