Denmark's justice ministry on Thursday said it had received Japan's extradition request for anti-whaling activist Paul Watson, who was detained in Greenland last month on an international arrest warrant.

Watson, the 73-year-old American-Canadian founder of the Sea Shepherd activist organization, was arrested on July 21 in Greenland, an autonomous Danish territory, over a 2010 altercation with Japanese whaling ships.

"The Ministry of Justice received a formal extradition request regarding Paul Watson from the Japanese authorities yesterday," the Danish justice ministry said in an email.

The ministry said it would forward the case to Greenland police, "unless the ministry on the present basis finds grounds to reject the extradition request beforehand."

If the case is forwarded to Greenland police, they will investigate "whether there is basis for extradition," including whether it is in accordance with the extradition act applicable to Greenland, the justice ministry said.

However, the ultimate decision on Watson's extradition will be made by Denmark's justice ministry, it added.

Watson was arrested after arriving in Nuuk, the capital of Greenland, when the ship John Paul DeJoria docked to refuel.

The vessel was on its way to "intercept" Japan's new whaling factory vessel in the North Pacific, according to the Captain Paul Watson Foundation (CPWF).

Japan is one of only three countries in the world to permit commercial whaling, along with Iceland and Norway.

French President Emmanuel Macron's office has asked Danish authorities not to extradite Watson, who has lived in France for the past year.