Anti-whaling activists in Australia have once again accused Japanese whaling ships of attacking ships belonging to a conservation group.

Paul Watson, the founder of an anti-whaling group called, Sea Shepherd has claimed that three ships of the group moved to cut access to the tanker Sun Laurel and imposed a blockade affecting Japanese factory ship Nisshin Maru. He added that the Nisshin Maru and its three harpoon ships attacked Sea Shepherd vessels Bob Barker, Steve Irwin and Sam Simon.

"The Nisshin Maru has rammed the Bob Barker and pushed it into the side of the Sun Laurel. Concussion grenades are being deployed against the Bob Barker, and near the tanker. It's a very intense situation," said Watson.

The blockade imposed by Sea Shepherd prevented Nisshin Maru from reaching the tanker Sun Laurel in the previous week. They are accusing the ship of being involved in dramatic collisions with Sea Shepherd vessels.

Sea Shepherd also said that earlier Japanese military icebreaker Shirase reached the location in Mackenzie Bay and a helicopter escort was flying over Sun Laurel. Shirase is operated by Japan Maritime Self-Defence Force and it is capable of carrying 250 people and three helicopters. Mr Watson said that the group is concerned that Shirase might be used against the vessels of Sea Shepherd in the area.