"We have asked the Netherlands to stop the pirate-like dangerous activities by Greenpeace, as their boat is registered in the Netherlands," said Hideki Moronuki, chief of the whaling section at Japan's Fisheries Agency.

"The latest collision was really dangerous although we were lucky no one was injured. If activists further escalate their violent action, ignoring the calls for restraint by all authorities, we have to think about taking tougher measures," he told AFP.

The Japanese demand followed a collision Sunday between the Japanese whalers' Nisshin Maru ship and Greenpeace's Arctic Sunrise, with each side saying the other is at fault.

The Japanese whaling authority, the Institute of Cetacean Research, has called on environmentalist groups Greenpeace and the more militant Sea Shepherd to "stop at once their dangerous and criminal actions."

The environmentalists have been trying to disrupt the hunt by putting activists in small inflatables between the harpooners and the whales.

The International Whaling Commission (IWC) imposed a moratorium on commercial whaling in 1986 but Japan has continued hunting for what it calls scientific research -- a claim rejected by critics.

Japan, where whale is part of the cuisine, makes no secret that the meat from the killing ends up on dinner plates here.

But Moronuki stood by Japan's stance that its mission was for research, noting that Tokyo had informed the IWC of its plans for the Nisshin Maru to "capture" 850 minke whales and 10 fin whales.

"If you want to get fundamental knowledge on the ecology of whales, such as sex, ages, what they eat and their state of nutrition, it is inevitable to cause whales' death during research," Moronuki said.

"There is a consensus among scientists that it is not true to say minke whales are on the verge of extinction," he added.

Minke whales are listed as "vulnerable" by the International Conservation Union.

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