Police in Greenland say they have apprehended veteran environmental activist and anti-whaling campaigner Paul Watson on an international arrest warrant issued by Japan.

Watson, a 73-year-old Canadian-American citizen, is a former head of the Sea Shepherd Conservation Society whose direct action tactics, including high-seas confrontations with whaling vessels, have drawn support from A-list celebrities and featured in reality television series Whale Wars.

He was arrested in the Danish territory on Sunday when his ship docked in Nuuk, Greenland’s capital, a police statement said. He later appeared before a district court looking into a request to detain him pending a decision on his possible extradition to Japan, the statement said.

On Monday, the Captain Paul Watson Foundation said in an emailed comment that he would be detained in Nuuk at least until August 15 after the court’s decision, to give the Danish justice ministry time to investigate the case and possible extradition.

He faces a maximum sentence of 15 years in prison in Japan, according to the foundation.

The organisation also said the Greenland court would not allow Watson’s release on bail as he was considered a flight risk.

The foundation said more than a dozen police officers boarded the ship when it stopped to refuel and led Watson away in handcuffs. The foundation said the vessel with 25 volunteer crew members was en route to the North Pacific on a mission to intercept a new Japanese whaling ship.

“The arrest is believed to be related to a former Red Notice issued for Captain Watson’s previous anti-whaling interventions in the Antarctic region,” the foundation said in an emailed statement on Sunday.

“We implore the Danish government to release Captain Watson and not entertain this politically motivated request,” Locky MacLean, the foundation director, said in the statement.

Neither the Japan Coast Guard nor Japan’s Foreign Ministry, which had issued the international warrant for Watson, confirmed they were negotiating Watson’s handover, but the coast guard, the primary investigative authority in Watson’s case in Japan, said on Monday that officials are on standby if a handover is ordered.

Greenland is an autonomous territory of Denmark. Japan does not have an extradition treaty with the European country and it is unknown if or when Watson would be handed over.

It is not the first time his tactics have brought him into conflict with authorities. He was detained in Germany in 2012 on a Costa Rican extradition warrant but skipped bail after learning that he was also sought for extradition by Japan, which has accused him of endangering whalers’ lives during operations in the Antarctic Ocean.

He has since lived in countries including France and the US.

Watson, who left Sea Shepherd in 2022 to set up his own organisation, was also a leading member of Greenpeace but left in 1977 amid disagreements over his aggressive tactics.

According to his foundation, Watson’s current ship, the M/Y John Paul DeJoria, was due to sail through the Northwest Passage to the North Pacific to confront a newly built Japanese factory whaling ship, “a murderous enemy devoid of compassion and empathy hell bent on destroying the most intelligent self-aware sentient beings in the sea”.