Canberra, Australia: Three anti-whaling activists boarded a Japanese vessel off southwest Australia yesterday as part of a campaign to stop whale hunting in Antarctic waters.

The three Australian men boarded the Shonan Maru No. 2 in early morning darkness as it tailed the Sea Shepherd Conservation Society's flagship the Steve Irwin, the conservation group said.

The three activists, who are members of an environmental group, said they were helping Sea Shepherd "end illegal whale poaching". The whale hunts, which Japan says are for scientific purposes, are allowed by the International Whaling Commission as an exception to the 1986 ban on whaling. But opponents say they are a cover for commercial whaling because whale meat not used for study is sold for consumption in Japan.

Glenn Inwood, spokesman for Japan's Tokyo-based Institute of Cetacean Research, which sponsors the annual whale hunt, confirmed that the three had boarded the vessel and were being questioned. The activists were not injured.

"I would describe them as volunteer detainees," Inwood said. Pete Bethune, a Sea Shepherd activist, boarded the same Japanese ship in 2010. Bethune, a New Zealander, spent five months in a Japanese jail before being convicted of an array of offences and deported.

Sea Shepherd founder Paul Watson, captain of the Steve Irwin, called on Australia's government to prevent the three Australian citizens from being taken to Japan.