A US judge refused Thursday to restrain a US-based environmental group from disrupting the activities of Japanese whalers, allegedly with violence.

Judge Richard Jones denied a request for a preliminary injunction sought by Japanese whalers against the Sea Shepherd Conservation Society, which is based in northwestern state of Washington.

The whalers sought a court order preventing the Sea Shepherd and its founder Paul Watson "from engaging in physical attacks on plaintiffs' vessels in the Southern Ocean," referring to the ocean encircling Antarctica.

Plaintiffs included the Institute of Cetacean Research, Kyodo Senpaku Kaisha, Ltd., Tomoyuki Ogawa ("Captain Ogawa"), and Toshiyuki Miura ("Captain Miura").

"Over the past few years, defendants have engaged in repeated, relentless violent attacks against plaintiffs in the Southern Ocean," read the injunction request, filed in Seattle.

These range "from ramming vessels, attempting to disable plaintiffs' ships by dragging fouling ropes in their path, firing acid-filled glass projectiles at plaintiffs' vessels and their crew and launching incendiary devices against the vessels and crew, exposing them to risk of fire and explosion."

This conduct "endangers the safety of the vessels and the Masters, crew, and researchers on board and is in violation of international and domestic law, let alone any rational standard of human conduct," they said.

In their Seattle court submission, the whalers said they were "entitled to be free from attack by what are essentially self-proclaimed pirates with a base in the state of Washington."

But rejecting their request, the judge said: "The Court hears argument of counsel and makes a tentative ruling denying the motion for preliminary injunction," adding that a full judgment will be issued at a later date.

Last month Japan's Fisheries Agency said anti-whaling activists threw paint and foul smelling acid at a whaling ship in the Antarctic ocean in a fresh bid to halt the annual hunt, officials said.

Two boats belonging to Sea Shepherd approached the Japanese whaling vessel Yushin Maru No. 2 (YS2) and launched 40 bottles containing paint and butyric acid, the agency said.

The Japanese whaling fleet, led by the 720-tonne Yushin Maru, was seen leaving the Japanese port of Shimonoseki on December 6 for the annual hunt, with security measures beefed up after clashes in previous years.

Their mission is officially said to be for "scientific research," with the fleet aiming to catch around 900 minke and fin whales, according to a plan submitted by the government to the International Whaling Commission.