A Norwegian court Friday sentenced two American anti-whaling activists to four months in jail for trying to sink a Norwegian whaling vessel.

But it was unclear how the sentences could be implemented since Paul Watson, leader of the environmental group Sea Shepherd, and his friend Lisa Distefano both live in the United States and were not present at their trial.The national news agency NTB said they were found guilty of assisting an effort to sink the whaling boat Nybraena in December 1992 to protest against Norway's decision to resume commercial whaling despite an International Whaling Commission moratorium on all commercial killing of whales. Norwegian fishermen killed 226 whales last year with exploding grenades.