A court in Greenland has extended the detention of anti-whaling activist Paul Watson for three more weeks, pending a decision on his possible extradition to Japan where he is wanted over an altercation with whalers.

Wednesday's decision by the Greenland court marks the fourth extension of his detention since Watson was arrested in July in Nuuk, capital of the Danish autonomous territory.

In a statement, Greenland police said: "The court in Greenland has today decided that Paul Watson shall continue to be detained until November 13, 2024 in order to ensure his presence in connection with the decision on extradition."

Police added that Watson had immediately appealed the decision.

Ahead of the hearing, Watson's lawyer Julie Stage outlined that her team would ask for his immediate release, adding: "But unfortunately, realistically, that may not happen."

Stage also said she was preparing an appeal to be filed with Denmark's Supreme Court over the Nuuk court's earlier ruling on 2 October to keep the 73-year-old in custody.

Watson was arrested on 21 July when his ship, the John Paul DeJoria, docked to refuel in Nuuk on its way to "intercept" a new Japanese whaling factory vessel in the North Pacific, according to the Captain Paul Watson Foundation (CPWF).

He was detained on a 2012 Japanese arrest warrant, which accuses him of causing damage to a whaling ship in the Antarctic in 2010 and injuring a whaler.

Watson's lawyers insist he is innocent and say they have video footage proving the crew member was not on deck when the stink bomb was thrown.