Updated

A U.S. appeals court ordered American anti-whaling activists to keep 500 yards away from Japanese whaling ships off Antarctica.

The 9th U.S. Circuit Court of Appeals issued an injunction against the Sea Shepherd Conservation Society, which sends vessels every December to disrupt whale killings by Japan's Institute of Cetacean Research.

The whalers sued Sea Shepherd last year to prevent the protesters from interfering, but the judge refused to grant the request.

The 9th Circuit ordered Sea Shepherd not to approach any of the Japanese vessels until it can rule on the merits of the whalers' appeal.

Japan's whaling fleet kills up to 1,000 whales a year for research. Whale meat not used for study is sold as food in Japan, which critics say is the real reason for the hunts.