The Sea Shepherd Conservation Society ship the Steve Irwin (foreground) collides with the stern of Japanese whaling ship the Yushin Maru 2 in the Southern Ocean

The Sea Shepherd Conservation Society ship the Steve Irwin (foreground) collides with the stern of Japanese whaling ship the Yushin Maru 2 in the Southern Ocean (REUTERS/Sea Shepherd Conservation Society/Adam Lau/Handout)

Japanese whalers have asked a U.S. court to block "sabotage" by Sea Shepherd activists who last season forced them to shorten their annual hunt in the Antarctic Ocean.

The Institute for Cetacean Research and Kyodo Senpaku, which owns the ships used for Japan's so-called scientific whaling programme, said on Friday they had filed a lawsuit against the Sea Shepherd Conservation Society (SSCS) and its founder, Paul Watson, in a Seattle district court.

The announcement follows news that some government funds earmarked for post-tsunami reconstruction will be redirected to beef up security for the whaling fleet.

"Sabotage activities against the research fleet by SSCS and Paul Watson have been escalating over several years," the whaling groups said. "Their actions are dangerous, life threatening and contrary to international law."

Sea Shepherd is a U.S.-based marine wildlife conservation group that says it uses "innovative direct-action tactics to investigate, document, and take action when necessary to expose and confront illegal activities on the high seas".

Japanese officials said they hoped the suit would send a clear message.

"With this as a turning point, I hope they stop disturbing us," said Michihiko Kano, Japan's Agriculture, Forestry and Fisheries Minister.

Japan said in October that it would tighten security for its fleet in the Antarctic this winter, including sending a patrol ship to protect crews.

One of three nations that hunt whales, Japan introduced scientific whaling to skirt a commercial whaling ban after a 1986 international moratorium.

It argues that it has a right to monitor the whales' impact on its fishing industry and cites a long history of whaling, as well as cultural traditions including eating whale meat.

Part of a third extra budget is set aside for security measures, and 498.9 billion yen of the 12.1 trillion yen extra budget is earmarked for fisheries-related reconstruction such as repairs of fishing ports damaged by the March 11 earthquake and tsunami.

The government said it hoped some 2.3 billion yen ($29.7 million) to be used for "measures to promote the stability of scientific whaling" would help the recovery of Ishinomaki, a city devastated by the tsunami.

Australia filed a complaint against Japan last year at the World Court in the Hague to stop Southern Ocean whaling. A ruling is not expected until at least 2013. ($1 = 77.5100 Japanese yen) (Writing by Elaine Lies; Editing by John Newland)