Japan's six-ship fleet has been prevented from whaling in the past week by anti-whaling protesters. Greenpeace has been trailing the fleet for several days, while Sea Shepherd protesters boarded a Japanese ship forcing it to stop whaling.
"Activists from the Greenpeace ship Esperanza today blocked the fleet's factory ship Nisshin Maru from being refueled in Antarctic waters by the Panamanian-registered vessel Oriental Bluebird," Greenpeace said in a statement.
"The activists ... placed their inflatable boat between the factory ship and refueling vessel, preventing them from coming alongside to refuel."
Japan's whaling association and fisheries agency both said they were not aware of the reported incident.
The militant Sea Shepherd Conservation Society has vowed more confrontations with Japan's whaling fleet, after two of its activists were held for two days after boarding the Yushin Maru No.2. The men were eventually released to an Australian fisheries ship and transferred back to the Sea Shepherd's Steve Irwin ship.
Japan and Sea Shepherd activists accused each other of "piracy and terrorism" during the two-day stand-off last week.
Steve Irwin skipper Paul Watson last year threatened to ram the Japanese flagship and collided with a harpoon vessel.
Japanese whaling officials have said they plan to try and exhaust the fuel supplies of the anti-whaling ships before they resume whaling. The Sea Shepherd ship has about two weeks of fuel left. Greenpeace won't say how much longer their ship can last.
Japan plans to hunt almost 1,000 minke and fin whales for research over the Antarctic summer, but has abandoned the cull of 50 humpback whales after international condemnation and a formal diplomatic protest by 31 nations.
Despite a moratorium on whaling, Japan is allowed an annual "scientific" hunt, arguing whaling is a cherished cultural tradition and the hunt is necessary to study whales. Its fleet has killed 7,000 Antarctic minkes over the past 20 years.
Reporting by Michael Perry; Editing by Bill Tarrant
© Reuters 2008