There are reports of fresh trouble between Sea Shepherd and Japanese whalers in the Southern Ocean .
Sea Shepherd says the factory ship Nissin Maru rammed one of its vessels, the Bob Barker, twice on Monday afternoon, causing it to collide with a tanker, the Sun Laurel.
Sea Shepherd also said a flash bang grenade was thrown by the whalers while it was attempting to block a refuelling operation.
Sea Shepherd also said a military icebreaker, the Shirase, has arrived to assist the whalers.
The Shirase can carry 250 personnel and three helicopters.
Sea Shepherd also said two of its ships, the Steve Irwin and Sam Simon, had their engine rooms flooded by water cannons.
Australian federal environment minister Tony Burke issued a please-explain to Japan about the ship's role.
"Japan has told the government that the Shirase is not involved in supporting (the) whaling fleet," Mr Burke said in a statement.