Japan launched a whaling mission on Wednesday with the target of killing 60 minke whales for what the government calls research, drawing immediate protests from environmentalists.

Four whaling ships and one designated research vessel set sail from Ayukawa port in northern Miyagi prefecture to hunt the giant sea mammals within 80 kilometres of its coast until late next month, the fisheries agency said.

Japan hunts whales using a loophole in a 1986 international moratorium on commercial whaling that allows "lethal research" on the giant mammals, and it makes no secret of the fact that the animals' meat is then sold as food.

Japanese whalers killed 680 of the animals in Antarctic waters in recent months on a hunt that the government also said served a scientific purpose.

"It's necessary to research whaling in the Pacific as the ecological system of whales in the Pacific is totally different from the one in the Antarctic," said Shigeki Takaya, a fisheries agency official.

Greenpeace, while staging no active protests this time, voiced its strong opposition to Japan's latest whaling mission.

"If Japan wants to simply conduct research, there is no need to kill (whales), either in the Pacific or the Antarctic," said Junichi Sato of Greenpeace Japan.

"For Japan, killing whales and producing whale meat comes first."

Greenpeace protested last week when Japan's fleet returned from its five-month Antarctic mission. The trip was marked by tense standoffs at sea, with the Sea Shepherd Conservation Society, a militant environmentalist group, forcing Japan to cut short its 100-day whaling mission by 16 days.

Due to the obstruction, the six ships caught 679 minke and one fin whale on the Antarctic mission, well below its planned haul of between 765 and 935 whales.

Japan launched the latest mission ahead of the International Whaling Commission's annual general meeting in June in Madeira, Portugal.

Japan defends whaling as part of its heritage and has threatened to leave the IWC if it does not shift to what Tokyo believes is its original purpose, managing a sustainable kill of whales.

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