The threat came from the Sea Shepherd Conservation Society, which has been hounding the whalers in its ship the Farley Mowat.

"Sea Shepherd Conservation Society believes it is time to escalate the confrontation with the Japanese whaling fleet and bring an end to the illegal and ruthless slaughter of defenseless whales in the Antarctic Whale Sanctuary," the group said in statement received here.

The statement quotes the group's founder and captain of the Farley Mowat, Paul Watson, as saying he was "tired of politicians being apologists for these criminals."

"We sideswiped the whaling supply ship Oriental Bluebird (Monday) and we intend to disable any pirate whaling vessel we find. We intend to uphold the laws protecting whales. This nonsense must be ended."

Watson, a founder member of the environmental group Greenpeace, left the organisation in 1977 after disagreements over tactics and has taken a more aggressive approach with Sea Shepherd.

Greenpeace has two vessels also harassing the six-ship Japanese whaling fleet in the Southern Ocean.

One of them, the Arctic Sunrise, collided with the Oriental Bluebird on Sunday. Each side blamed the other for the collision.

The International Whaling Commission imposed a moratorium on commercial whaling in 1986 but Japan has continued hunting for what it calls scientific research -- a claim rejected by critics.

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.