Sea Shepherd founder Paul Watson will not be extradited to Japan to face charges relating to an incident aboard a whaling vessel in 2010, Denmark's justice ministry has decided.

Mr Watson, 74, has been detained in Greenland, an autonomous territory of Denmark, since July, after having been arrested on an international warrant issued by Japan in 2012. 

The warrant accused him of causing damage to a Japanese whaling ship in the Antarctic in 2010, and injuring one crew member.

He was released from detention in Nuuk, Greenland's capital, on Tuesday.

The development came after Mr Watson's lawyer, Julie Stage, announced he would not be extradited to Japan over the charges against him.

According to documents viewed by news agency AFP, Denmark's justice ministry reached its decision while considering the duration of Watson's detention following his arrest and the time it would take for a possible extradition to be carried out.

The ministry also considered "the fact that the acts for which extradition is sought are more than 14 years ago, and the nature of the acts in general".

"The decision is based on an overall assessment of the circumstances of the specific case," the ministry said in a statement.

Mr Watson is the founder of the anti-whaling organisation Sea Shepherd, and has starred in the reality TV series Whale Wars.

He split from Sea Shepherd in 2022, alleging he had been told his reputation was incompatible with where the organisation was headed.

Mr Watson was arrested on July 21 this year when his ship was on its way to "intercept" a new Japanese whaling factory vessel in the North Pacific, according to the Captain Paul Watson Foundation.

Tokyo accuses Mr Watson of injuring a Japanese crew member with a stink bomb intended to disrupt the whalers' activities during a Sea Shepherd clash with the Shonan Maru 2 vessel in 2010.

Mr Watson's lawyers have said they have video footage proving the crew member was not on deck when the stink bomb was thrown.

They accused Japanese authorities of attempting to silence his work, and vowed that he would "resume his fight for respect for nature".

In a rare public comment on the case, Japanese Foreign Minister Takeshi Iwaya has said that the extradition request was "an issue of law enforcement at sea rather than a whaling issue".

Danish Minister of Justice Peter Hummelgaard, also stated that "this decision does not mean that Denmark shares the concerns that have been raised in certain circles about the Japanese legal system and the protection of human rights in Japan in relation to this specific case".

Mr Watson's lawyers said they would fight the international arrest warrant and a separate "red notice", which compels law enforcement authorities around the world to locate and arrest a person.

Reuters/AFP