TOKYO (AFP) - Japan on Monday said it was asking the Netherlands to take "practical measures" against a Dutch-registered vessel that collided with a Japanese whaling ship in the Southern Ocean.
The Bob Barker, belonging to militant anti-whaling campaigners Sea Shepherd, came into contact with a Japanese harpoon vessel on Sunday as it tried to interrupt the hunt.
Each side has blamed the other for the collision.
In Tokyo, Chief Cabinet Secretary Yoshihide Suga condemned the group, saying it was responsible for the accident.
"The sabotage activity was extremely dangerous," Mr Suga told reporters.
"It is unforgivable," the top government spokesman said without elaborating. "As a government, we are asking the Netherlands, where the ship is registered, to take practical measures."
Australia's Environment Minister Greg Hunt said the alleged collision occurred in New Zealand waters and sounded a warning to the warring groups.
"This must be a message to both parties - whalers and protesters - these are dangerous waters, nobody can play any games with safety, nobody can play any games with international law," Mr Hunt said.
"Everyone must abide by the law and of course if there is evidence that either party has breached international maritime law we will raise it."
Sea Shepherd has insisted that the Japanese ship rammed the Bob Barker during a coordinated attack as the Japanese fleet's three harpoon ships tried to drive the campaigners away from the factory ship Nisshin Maru.
The group said the Japanese had attempted to damage the Sea Shepherd ships' propellers with steel cables, had thrown projectiles including grappling hooks at a second Sea Shepherd ship, the Steve Irwin, and fired water cannon at the Bob Barker's crew as they tried to cut the cables from a small boat.
Bob Barker captain Peter Hammarstedt said the Sea Shepherd vessels were "unprovokedly attacked" by the Japanese harpooners in a "ruthless" fashion.
A Japanese fisheries agency official said no crew aboard the whalers had been hurt and all its vessels were able to continue sailing normally.
High-seas confrontations are common between Sea Shepherd and the Japanese, who hunt whales in Antarctica under a "scientific research" loophole in the international moratorium on whaling.
In 2010 a collision resulted in the sinking of Sea Shepherd's speedboat Ady Gil.