Story highlights The two sides trade accusations over who caused ships to collide

The incident follows a previous high seas clash a week ago

Environmental groups face off each year with Japan's whaling vessels

Environmental activists and Japanese whaling authorities have reported fresh clashes in Antarctic waters, with each side accusing the other of causing dangerous collisions between ships.

The conflicting claims follow harsh words and threats of legal action exchanged between the two sides last week amid activists' attempts to impede the Japanese vessels' annual hunt for whales in the Southern Ocean.

The Institute of Cetacean Research (ICR) -- which conducts whaling activities under the authority of the Japanese Ministry of Agriculture, Forestry and Fisheries -- accused ships from the environmental group Sea Shepherd of "sabotage."

During an attempt by the whaling fleet's main ship, the Nisshin Maru, to refuel on Monday, Sea Shepherd vessels "repeatedly forced their way" between the Japanese ship and the fuel tanker, ramming into them in the process, the ICR said. It released short videos showing collisions between vessels.

Competing accounts

But Sea Shepherd's Australian division countered with a different version of events, saying that the Nisshin Maru had caused the collisions.

Photos: Japan, Australia in ship dispute Photos: Japan, Australia in ship dispute Japan whaling clashes – In these photos provided by Japan's Institute of Cetacean Research, SS activists onboard the inflatable boat "Gemini" sent from the Bob Barker deploy a wire-entwined rope near the Yushin Maru vessel, aiming to entangle its rudder and propeller, on Monday, February 25. Hide Caption 1 of 5 Photos: Japan, Australia in ship dispute Japan whaling clashes – After ramming the Nisshin Maru, the SS Bob Barker rammed the supply tanker port stern on February 25, according to the ICR. Hide Caption 2 of 5 Photos: Japan, Australia in ship dispute Japan whaling clashes – Sea Shepherd vessels surrounding a red supply vessel are pictured on Wednesday, February 20. From lower right to left: SS Bob Barker, SS Steve Irwin, SS Sam Simon. Hide Caption 3 of 5 Photos: Japan, Australia in ship dispute Japan whaling clashes – The SS Bob Barker forced its way between the black Nisshin Maru and the red supply vessel on February 20, the ICR said. Hide Caption 4 of 5 Photos: Japan, Australia in ship dispute Japan whaling clashes – In doing so, the SS Bob Barker collided with the supply vessel's port side, the ICR said. Hide Caption 5 of 5

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The group said that a Sea Shepherd ship, the Bob Barker, became "sandwiched" between the Nisshin Maru and the fuel tanker after positioning itself to block the refueling.

"In the turbulence of the combined wake, the Bob Barker was slammed back and forth between the Nisshin Maru and the fuel tanker," Sea Shepherd said.

It also claimed the Nisshin Maru rammed another Sea Shepherd vessel, the Sam Simon, "causing hull damage along most of the port side of the ship and smashing their satellite communications dome."

No injuries were reported in the clashes, but the Nisshin Maru "decided to interrupt her refueling procedure due to the extremely dangerous and foolhardy behavior" of the Sea Shepherd vessels, the ICR said. Crews are still determining to what extent the Nisshin Maru and the refueling ship were damaged, it said.

The two sides also traded accusations about the use of water cannon and ropes that snarl up ships' propellers.

Sea Shepherd says the fuel tanker's presence in the area is illegal, but the ICR says it is "essential for the safe navigation" of its ships, which are carrying out a "perfectly legal activity."

Legal threats

The Australian government last week called the Japanese activities in the Southern Ocean "unacceptable" and vowed to press on with an international legal action to stop the annual whale hunt. Those comments came after reported clashes in which Sea Shepherd vessels blocked a previous refueling attempt.

Sea Shepherd said the Japanese ships had intruded into Australian territorial waters and breached international and Australian law.

But the ICR says a U.S. court has banned Sea Shepherd from threatening whaling ships' operations or sailing within 500 yards them. It said it will provide "additional evidence" to the court about the latest incident.

Prime Minister John Key of New Zealand on Tuesday called for "cool heads" to prevail in the tense situation in the Southern Ocean, local broadcaster TVNZ reported.

Japan annually hunts whales despite a worldwide moratorium, utilizing a loophole in the law that allows for killing the mammals for scientific research. Whale meat is commonly available for consumption in Japan.