Police raided five places including the environmental group's Japan headquarters in Tokyo's bustling Shinjuku district, officials said.

Police arrested Junichi Sato, 31, a prominent voice in the media against whaling, and fellow Greenpeace member Toru Suzuki, 41, a police spokesman said.

Greenpeace, along with Western countries led by Australia, is strongly opposed to Japan's whaling programme, which kills some 1,000 of the ocean giants a year.

The Japanese government, which says whaling is part of the culture, carries out the hunt using a loophole in a 1986 international moratorium that allows "lethal research" on whales.

Last month, Greenpeace said its four-month investigation revealed that Japanese whalers took home whale meat from the country's annual "research" hunt in the Antarctic and were selling it on the black market.

It intercepted one box of meat as part of its probe and handed it to prosecutors in Tokyo. The group filed a complaint against 12 crew of a Japanese whaling ship whom it accused of stealing the meat.

A spokesman for police in northern Aomori prefecture, where the seizure took place on April 16, said that Sato and Suzuki were arrested for "illegally obtaining a cardboard box and trespassing."

Greenpeace protested against the arrests, saying that it obtained the whale meat was part of a legitimate investigation.

"Without taking such action, we couldn't have filed an accusation over the embezzlement of whale meat," Kazuo Hizumi, a lawyer for Greenpeace Japan, told reporters at the headquarters.

"The raids must not affect the investigation into the embezzlement accusation," the lawyer said.

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