MELBOURNE - Environmental group Greenpeace said on Saturday one of its ships has located the Japanese whaling fleet in the Southern Ocean and is pursuing it.

"If they stop to whale, then we will intervene," Greenpeace Australia chief executive Steve Shallhorn told Reuters.

He said the Japanese fleet of six would be prevented from whaling while it was being followed by the Greenpeace ship, the Esperanza.

"As long as we are in pursuit, they won't be able to whale. It's a bit of a marathon out there," Shallhorn said.

Japan's whaling fleet plans to hunt 935 minke whales and 50 fin whales for research over the Antarctic summer, but recently abandoned plans to hunt 50 humpback whales after international condemnation and a formal diplomatic protest by 31 nations.

Yushin Maru, a boat of the Japanese whaling fleet, is seen in the Southern Ocean Whale Sanctuary by Greenpeace ship Esperanza January 12, 2008. Japan's whaling fleet plans to hunt 935 minke whales and 50 fin whales for research over the Antarctic summer, but recently abandoned plans to hunt 50 humpback whales after international condemnation and a formal diplomatic protest by 31 nations. [Agencies]

Greenpeace said on its Web site that activists plan to put inflatable boats between the whalers' harpoons and the whales if the fleet begins whaling.

"If they try to start whaling, then we will do everything that we can to take peaceful direct action to stop that," Esperanza crew member Sara Holden told Australian Broadcasting Corp radio.

An Australian fisheries ship set out last week in pursuit of Japan's whaling fleet near Antarctica to gather evidence for an international court challenge to halt the yearly slaughter.

The icebreaker Oceanic Viking, used for customs and fisheries policing, left a naval base near Perth late on Tuesday to find and track the fleet in the Southern Ocean for up to 20 days.

Australian government minister Chris Bowen urged the Greenpeace activists to show restraint.

"Their own personal safety is at risk and the personal safety of others is at risk," Bowen, Assistant Treasurer, told reporters.

Japan has long resisted pressure to stop scientific whaling, insisting whaling is a cherished cultural tradition. Its fleet has killed 7,000 Antarctic minkes over the last 20 years.