The protesters had been running their boat between the Nisshin Maru and the Oriental Bluebird fuel ship for about an hour today, said Greenpeace spokesman Dave Walsh from aboard the Greenpeace ship Esperanza.

Mr Walsh said the refuelling was occurring south of the 60-degree line in the Southern Ocean, in breach of the Antarctic Treaty.

Greenpeace said the Panamanian-registered Oriental Bluebird also did not have a Japanese government permit to be a part of the whaling fleet.

The Esperanza radioed a statement to the Bluebird calling on the vessel to leave Antarctic waters.

"A refuelling operation within the treaty area would be contrary to the spirit of the Antarctic Treaty."

The fuel ship had responded by telling the activists to keep out of the way, Mr Walsh said.

He said two of the fleet's three catcher boats were also in the area.

Greenpeace has been tailing the Nisshin Maru for 11 days, during which time it says no whaling has taken place.

Mr Walsh said the Esperanza had not seen the Australian customs vessel Oceanic Viking or Sea Shepherd Conservation Society ship Steve Irwin.

The Steve Irwin has been trying to find the fleet after losing the whalers since two crew members last week were returned from catcher boat Yushin Maru No. 2.

Greenpeace refuses to share co-ordinates with Sea Shepherd because of differences over protest tactics.