Anti-whaling group Sea Shepherd and Japanese whalers are again colliding in the Southern Ocean south of Australia, with the conservation group accusing the Japanese of illegally bringing in a military-style ship to the conflict.
Sea Shepherd says the factory ship Nisshin Maru rammed Sea Shepherd's vessel Bob Barker twice on Monday afternoon, causing it to collide with the tanker Sun Laurel.
A "flash bang grenade" has been thrown by the whalers, it says.
However, in one video, supplied by the Japanese Institute of Cetacean Research (ICR), it does appear a Sea Shepherd ship – painted in camouflage and with shark teeth on its bow – rams a Japanese vessel as it moves between two ships.
The ships have collided despite a US court ordering Sea Shepherd to stay at least 500 yards away from the Japanese ships.
Japan's Maritime Self Defence Force 12,500-tonne Shirase, which can carry three helicopters, is now also in the area.
Sea Shepherd's Paul Watson says the presence of a Japanese military ship is highly concerning, as that would be a violation of the Antarctic Treaty.
The ship had dropped commandos on Sun Laurel by helicopter, he told Radio New Zealand.
"But we did prevent them from refuelling and we also prevented them from taking any whales."
The ICR, in a statement, accused Sea Shepherd of "malicious and inconceivably obstructive" sabotage as the Japanese went about legal whaling operations.
The Bob Barker and Sam Simon had repeatedly forced their way between the Nisshin Maru and the supply tanker and rammed the Japanese ships numerous times, threatening their safety, it said.
The ICR also said the fuel it was trying to transfer was approved for use in Antarctic waters, and was safely conducted through a hermetically sealed fuel transfer system.
Australia's environment minister Tony Burke issued a please-explain to Japan about the ship's role, suggesting it was exploiting a loophole by assisting the Korean tanker rather than the Japanese whalers directly.