An anti-whaling activist group says three of its members were injured Wednesday during clashes with Japanese whalers off the coast of Antarctica.

The Sea Shepherd group said two activists suffered deep bruising after being struck in the shoulder with iron grappling hooks. Another received lacerations after being stabbed in the face with a bamboo pole.

The U.S.-based group said its boats were attacked while attempting to slow down the Japanese whaling vessel Yushin Maru No. 2 in the Southern Ocean early Wednesday.

But Japan's Institute of Cetacean Research said the whalers were acting in self-defense. It said its crew used bamboo poles to push away the Sea Shepherd boats after the activists attempted to disable the Japanese ship's rudder and propeller.

Video released by the whalers appears to show the activists throwing small objects at the Japanese vessel, while the whalers respond with water cannons.

The U.S.-based group regularly sends small boats to harass the Japanese fleet during its annual whale hunt. It is known to use stink bombs, dye markers, laser beams and other objects to attempt to disrupt the Japanese whalers.

The Japanese Coast Guard earlier warned that it would deploy a number of vessels to protect the expedition during this season's harvest.

Commercial whaling is banned under an international treaty, but Japan continues to hunt using a loophole that allows whaling in the name of science, a practice condemned by environmentalists and anti-whaling nations.