Japan's whalers have won an injunction in a United States court against Sea Shepherd, restraining the anti-whaling group from attacking their ships in the Southern Ocean.

The decision by the US Ninth Circuit Court of Appeals was described as "somewhat astonishing" by Sea Shepherd leader Paul Watson on Tuesday.

It follows an appeal to the court by Japan's Institute for Cetacean Research against the decision of a US District Court judge refusing an injunction earlier this year.

Chief Judge, Tashima Kozinski said in the decision that Sea Shepherd, Mr Watson, and anyone acting for them, were "enjoined from physically attacking any vessel engaged by Plaintiffs the Institute of Cetacean Research, Kyodo Senpaku Kaisha, Lt., Tomoyuki Ogawa or Toshiyuki Miura in the Southern Ocean."

Kyodo Senpaku Kaisha operates the whaling fleet for the ICR, While Mr Ogawa and Mr Miura are believed to be senior officers.