Japanese whalers and militant conservationists have been involved in dangerous clashes in icy waters off Antarctica, with both sides accusing the other of ramming their vessels.
Veteran anti-whaling campaigner Paul Watson said the Japanese factory ship the Nisshin Maru rammed the Sea Shepherd Conservation Society's much smaller vessel the Bob Barker in the incident on Monday.
But on its website, Japan's Institute of Cetacean Research accused several Sea Shepherd boats of slamming into the Nisshin Maru as the vessel attempted to refuel with her supply tanker the Sun Laurel.
"It was five hours of intense confrontation," Watson told AFP from on board the Sea Shepherd vessel the Steve Irwin.
"We took up our positions to block their approach to the (fuel tanker) Sun Laurel and they rammed the Bob Barker twice, causing considerable damage, and then they pushed it into the side of the Sun Laurel."
Watson said the Japanese threw stun grenades and fired a water cannon at his boat and damaged another Sea Shepherd vessel, the Sam Simon, but there were no injuries to Sea Shepherd crew.
"It was extremely dangerous," he said.
"I can't tell you how intimidating it is to have a 12,000 tonne ship coming at you and trying to slam into the side of you.
"Their contention that we rammed them is just ludicrous. We would just bounce off them."
The Institute of Cetacean Research said the Japanese vessels were "again subject to sabotage by the Sea Shepherd ships Steve Irwin, Bob Barker and Sam Simon".
"During their obstruction to refuelling operations the Sea Shepherd vessels rammed into... the Nisshin Maru and the supply tanker," it said.
"During the attack, the Nisshin Maru used her water pump as a preventive measure to make Sea Shepherd vessels refrain from further approaching, and repeatedly broadcasted a warning message to stop them."
It said no crew on its side were injured but accused the Sea Shepherd campaigners of "extremely dangerous and foolhardy behaviour" that threatened the lives of those on board the vessels.
Japan's fisheries agency separately issued a statement saying Sea Shepherd boats rammed the Japanese whaling ship when it was getting fuel.
The Sea Shepherd Conservation Society has chased the Japanese fleet hunting whales off Antarctica for several years in a bid to stop the animals being slaughtered.
The latest skirmish follows a similar incident in the remote Southern Ocean last week that prompted calls for Australia to intervene.
An official from Japan's fisheries agency said Tokyo "has frequently requested that the Australian government take measures to prevent such incidents through various diplomatic routes".
"We can't disclose details of our requests including the timing because of diplomatic sensitivities," he said.
Canberra is strongly opposed to whaling but prefers to press its case through the International Court of Justice.
"The court is the best place to resolve a serious disagreement between governments," Environment Minister Tony Burke said Tuesday, adding that the court was getting closer to full hearings on the case.
"As I have said before there is nothing scientific about harpooning a whale, chopping it up and putting it on a plate."
Japan says it conducts vital scientific research using a loophole in an international ban on whaling, but makes no secret of the fact that the mammals ultimately end up as food.