Hong Kong (CNN) -- 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.
But Sea Shepherd's Australian division countered with a different version of events, saying that the Nisshin Maru had caused the collisions.
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."
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.
Each year, environmental groups such as Sea Shepherd face off with Japan's hunters in a high seas drama that has led to collisions of ships, the detaining of activists and smoke bombs fired back and forth between the groups.
CNN's Yoko Wakatsuki in Tokyo, and Neda Farshbaf in Atlanta contributed to this report.