Japanese whalers and militant conservationists have again 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 in the incident on Monday the Japanese factory ship the Nisshin Maru rammed the Sea Shepherd Conservation Society's much smaller vessel the Bob Barker.
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 used a water cannon on 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 onboard 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 slaughter of the mammals.
The latest skirmish follows a similar incident in the remote Southern Ocean last week which prompted calls for Australia to intervene.
Canberra is strongly opposed to whaling but prefers to press its case through the International Court of Justice.
Environment Minister Tony Burke has described Japan's whale hunt as cruel and unnecessary but has so far rejected calls to send an Australian government vessel to monitor the hunt.
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.
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.