The International Whaling Commission has accused campaigners protesting against Japan's whaling fleet of creating danger in the Antarctic Ocean.
The regulator rebuked U.S. anti-whaling group the Sea Shepherd Conservation Society on Saturday for "jeopardizing safety at sea," following a three-day meeting in London.
Protesters aboard Sea Shepherd's vessel, the Steve Irwin, have been involved in a series of clashes with Japanese vessels taking part in the country's whaling research program.
The commission "called upon the Sea Shepherd Conservation Society to refrain from dangerous actions that jeopardize safety at sea, and on vessels and crews concerned to exercise restraint".
"The commission and its contracting governments do not condone and in fact condemn any actions that are a risk to human life and property in relation to the activities of vessels at sea," it said in a statement.
Sea Shepherd and other anti-whaling groups have repeatedly harassed the Japanese whaling fleet to interfere with the hunt. Japan kills about 1,000 whales every year under an internationally-approved research program.
Japan has accused the activists of terrorist tactics and insists it only wants to take the types of whales that are plentiful.
The meeting came as strains between members of the commission worsen.
Japan, Norway and Iceland lead a group keen to reintroduce commercial whaling, but other members, including Britain, remain firm in their stance against it.
The polarization has made decision-making in the commission — which is designed to conserve whale stocks and regulate the development of the whaling industry — increasingly difficult.
The commission said it would consider using small negotiating groups, adopting cooling-off periods when problems arise, and reducing the use of voting to help aid progress.
Despite the rebuke, Sea Shepherd would continue its actions in the Southern Ocean, said Paul Watson, captain of the Steve Irwin.
"This is the 21st century, and the IWC should be an organization to protect the world's whales from this barbaric practice," he said.
"Here they are condemning us for throwing stink bombs, but the Japanese are attacking endangered whales in violation of an Australian court order — they are no different to poachers."