Anti-whaling campaigner Paul Watson has been ambushed and arrested in Denmark on an international arrest warrant believed to have been issued by Japan.

The Greenpeace co-founder and Sea Shepherd founder was reportedly handcuffed and arrested by 14 police officers and SWAT team members after his ship reached port in Greenland, an autonomous Danish territory. Photos provided to Yahoo News by Watson’s newest venture Neptune’s Pirates and the Captain Paul Watson Foundation show a stunned Watson being forced into a van early Sunday morning (local time).

It is believed that a Red Notice – an international arrest warrant – was issued for Captain Watson’s previous anti-whaling campaign, which targeted Japan’s so-called scientific research program in the Antarctic region. Japan’s program was declared illegal by the International Court of Justice in 2014, and the country began to withdraw from hunting in its own territorial waters.

Related: ‘Absurd’ whale product tested in Japanese vending machines

Fears Paul Watson could die in prison if sent to Japan

Rob Read, COO of Neptune’s Pirates UK, said Watson’s supporters were in shock. There are fears the 73-year-old Watson could die in prison if he is transported to Japan.

“Paul could face 15 years in prison, probably life. (It was) a total ambush by Japan using an unpublished Interpol warrant that was filed in March of this year,” Read told Yahoo News via text message.

Denmark allows its self-governing archipelago, the Faroe Islands, to hunt whales and dolphins, which Neptune’s Pirates has actively campaigned against. Read, who has led the campaign, said that Denmark as a European nation has a duty to protect whales.

“The arrest was arranged in collaboration with Denmark just as Paul was sailing again to oppose Japanese whaling,” Read said.

More about whales and dolphins

The reason Paul Watson went to Japan

Watson was aboard his 230-foot flagship, the M/Y John Paul Dejoria, planning to intercept and blockade the new Japanese whaling ship when he was arrested.

The mission was announced after Japan announced it had added a new species to its list of animals killed this year: the fin whale, which is the species that has been killed for the longest time after the blue whale.

Colleagues on board the ship claim that a police officer told them: “We came here and arrested Paul Watson on an international arrest warrant from Japan.”

The Neptune Pirates said in a statement that they have no way of contacting Watson.

Locky MacLean, operations director of the Captain Paul Watson Foundation, said the arrest left the crew “completely shocked”.

“The Red Notice disappeared a few months ago. We were surprised because it could have been erased or classified. We now understand that Japan classified it to give Paul a false sense of security. We implore the Danish government to release Captain Watson and not to honor this politically motivated request,” he said in a statement.

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