Militant anti-whaling campaigners vowed more confrontations with Japan's whaling fleet near Antarctica on Friday, while the whalers aimed to exhaust the protest ships' fuel supplies to force them out of the area.

Whaling was to resume after the return to their ship of two Sea Shepherd Conservation Society activists, who were detained after boarding a Japanese harpoon ship on Tuesday.

Australian Benjamin Potts and Briton Giles Lane were picked up by an Australian fisheries icebreaker from the Yushin Maru No.2 in the Southern Ocean early on Friday and greeted back aboard their protest vessel, Steve Irwin, as heroes.

"They've been on a hunger strike since they were taken," Sea Shepherd spokesman Jonny Vasic told Reuters. "It was well worth the cost of saving whales."

Potts said Sea Shepherd would continue protests as the Yushin Maru headed back to the rest of the six-ship Japanese fleet to resume whaling until the end of the season next month.

Activists chased the whaler after the release of the pair, attempting to foul its propeller.

"We'll continue to harass the Japanese fleet and prevent them from whaling," Potts told Australian radio.

But a spokesman for the whaling fleet of three hunting ships, observer vessels and a factory ship said the Japanese were aiming to force the protesters to run out fuel by making them follow the fleet, prompting the protesters return to Australia.

"Eventually they will run out of fuel and both Greenpeace and Sea Shepherd will have to return to Melbourne," Glenn Inwood told Reuters. "That's probably the safest option for everyone as Japan can resume the programme in safety," Inwood said.

Vasic said the Sea Shepherd vessel had about two weeks' fuel left. Greenpeace wouldn't say how much longer their protest ship could last.

"We'll stay down here as long as we can and crawl into port on the last fuel vapours," Greenpeace chief executive Steve Shallhorn said.