Jan. 22 (Bloomberg) -- Japan's whaling fleet has stopped hunting because a Greenpeace vessel has been preventing harpoon boats from transferring their catch to the factory ship, the government said.

``It is very difficult to resume hunting when there is a ship that may interfere with our activity,'' Toru Shirasu, the administrative vice-minister of Agriculture, Forestry and Fisheries, said yesterday in Tokyo.

The Greenpeace ship Esperanza has been chasing the factory ship Nisshin Maru for 10 days, and has stopped the entire whaling operation, Greenpeace said yesterday in a statement.

The environmental group said on Jan. 12 that the Esperanza confronted Japan's whaling fleet in the Southern Ocean Whale Sanctuary after a 10-day search in Antarctic Waters.

``With the factory ship out of commission, no whales have been killed by the hunter ships as they would not be able to transfer their catch,'' Greenpeace said yesterday.

Shirasu said his ministry is working with the Foreign Ministry to deal with the situation, according to a transcript of his statement posted on the ministry Web site.

Japan is under increasing pressure from environmental groups to stop hunting whales. Last week, the Sea Shepherd Conservation Society vowed to keep chasing Japan's fleet across the Southern Ocean after two of its members who boarded a harpoon ship were freed.

Australian Benjamin Potts and U.K. citizen Giles Lane were detained after they boarded the Yushin Maru No. 2 with a letter demanding Japan call off its annual hunt. They were transferred to an Australian customs vessel and returned to their ship.

Japanese ships head to Antarctica in November each year to kill as many as 1,000 minke and fin whales in the name of research of whaling populations.

Research whaling is allowed under the terms of a global moratorium on commercial whaling imposed by the International Whaling Commission in 1986. Japan had planned to kill as many as 1,035 whales in the current expedition, the most since it began what it calls scientific hunts in 1987. The whaling fleet set sail from Japan on Nov. 18.

Japan abandoned a plan to resume culling humpback whales under pressure from Australia, New Zealand, the U.S. and the European Union.

Shirasu said yesterday Japan's food culture should be respected, adding that whale meat is healthy because it is low in fat and high in protein. ``We seek to eventually resume commercial whaling,'' he said.

To contact the reporter on this story: Tak Kumakura in Tokyo at tkumakura@bloomberg.net

Last Updated: January 21, 2008 17:43 EST