The decision by Rakuten comes soon after the UK-based Environmental Investigation Agency (EIA) exposed the company as the world’s biggest online retailer of whale products and elephant ivory.

Rakuten said it had asked sellers to cancel sales of whale meat products on its website “in accordance” with the ICJ ruling. Monday’s verdict in the Hague, however, did not cover whale meat sales in Japan, which are legal, or the country’s slaughter of a smaller number of whales in the north-west Pacific and in its own coastal waters.

Clare Perry, an EIA senior campaigner, said: “The removal of thousands of ads for whale products is a very welcome step and a clear recognition by Rakuten that selling the meat of endangered and protected whales and dolphins is seriously harmful to both its global reputation and customers’ health." In its Blood E-Commerce report [PDF] the conservation group said tests had revealed that some cetacean products advertised by Rakuten contained levels of mercury up to 20 times higher than the Japanese regulatory limit.

Rakuten’s acquisitions include Buy.com (now Rakuten Shopping) in the US and Play.com in the UK. It owns the Canadian e-book reader Kobo and is a major shareholder in Pinterest. “Rakuten, which has expanded its global presence in recent years, has also requested these merchants to remove all related items from their online shops within the next 30 days,” the firm said.

Monday’s ICJ ruling, in support of a four-year legal campaign by the Australian government, this week prompted Japanese authorities to call off next winter’s whale hunt in the Antarctic.

It is the first time the Antarctic hunt, during which harpoon vessels target almost 1,000 mainly minke whales, has been cancelled in more than a quarter of a century.

Japan launched its “scientific” whaling programme after the International Whaling Commission banned commercial whaling in 1986.

But on Monday a majority of judges at the UN court agreed with Australian claims that Japan had failed to demonstrate that the slaughter was of any scientific value.

Until recently Rakuten's website carried more than 28,000 advertisements for elephant ivory and 1,200 for whale products, according to the EIA and the Humane Society International.

Many of the whale products originated from species that have been protected since the 1986 moratorium. Rakuten’s sales ban covers not only the mammals’ meat but also skin, bone and other products.

Campaigners said they now expected the online retailer to add ivory to its list of banned products. “Japan is awash with illegal ivory trade and Rakuten's thousands of ivory ads help fuel the mass slaughter of elephants across Africa,” said Allan Thornton, the EIA president. “We appeal to Rakuten to help protect elephants by immediately banning all ads for ivory products.”