Greenpeace claimed on Sunday that its protest ship Esperanza had chased Japanese ships out of Antarctic waters where they have been hunting nearly 1,000 whales.
It said the Esperanza, which found the Japanese fleet on Saturday after 10 days of searching in the Southern Ocean, had driven the whalers out after a high-speed chase over hundreds of miles through fog and increasingly rough seas.
A Greenpeace statement said the Esperanza pursued the Japanese factory ship Nisshin Maru over the 60 degrees latitude mark - the boundary of the whale hunting grounds - followed by the catcher vessel Yushin Maru.
"We came here to stop the fleet from whaling and we have done that," Greenpeace Japan campaigner Sakyo Noda said from the Esperanza.
But the Greenpeace statement said it was suspected that the fleet was planning to refuel soon and offload whale meat that had already been processed onto a Panamanian-registered tanker Oriental Bluebird.
The Japanese have announced that they are trying to kill 935 minke whales and 50 endangered fin whales in this year's so-called scientific research programme.
After international protests last month, they abandoned plans to also catch 50 threatened humpback whales.
New Zealand and Australia have led an international campaign to stop the Japanese programme, which they claim is a front for commercial whaling.
"There are already around 4,000 tons of whale meat stockpiled in Japan from previous expeditions - clearly showing there is no appetite for it," Greenpeace said.
The president of the Japan Whaling Association, Keiichi Nakajima, said in a statement from Tokyo that the research programme was "perfectly legal" under an international convention for the regulation of whaling and warned Greenpeace to stay away from its vessels.
"Past activities of Greenpeace have been responsible for vessel collisions that risk the lives and safety of our researchers and crew and are illegal under international maritime law," he said. ( Dpa )