A beluga whale found off Norway's coast wearing a special Russian harness was probably trained by the Russian navy, a Norwegian expert says.
Marine biologist Prof Audun Rikardsen said the harness had a GoPro camera holder and a label sourcing it to St Petersburg. A Norwegian fisherman managed to remove it from the whale.
He said a Russian fellow scientist had told him that it was not the sort of kit that Russian scientists would use.
Russia has a naval base in the region.
The tame beluga repeatedly approached Norwegian boats off Ingoya, an Arctic island about 415km (258 miles) from Murmansk, where Russia's Northern Fleet is based. Belugas are native to Arctic waters.
Norway's public broadcaster NRK has put out a video showing the beluga's harness being released.
Prof Rikardsen told the BBC that the harness "was attached really tightly round its head, in front of its pectoral fins and it had clips". He said there was a GoPro attachment, but no camera.
"A Russian colleague said they don't do such experiments, but she knows the navy has caught belugas for some years and trained them - most likely it's related to that," he said.
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A Russian reserve colonel, who has written previously about the military use of marine mammals, shrugged off Norway's concern about the beluga. But he did not deny that it could have escaped from the Russian navy.
Interviewed by Russian broadcaster Govorit Moskva, Col Viktor Baranets said "if we were using this animal for spying do you really think we'd attach a mobile phone number with the message 'please call this number'?"
"We have military dolphins for combat roles, we don't cover that up," he said.
"In Sevastopol (in Crimea) we have a centre for military dolphins, trained to solve various tasks, from analysing the seabed to protecting a stretch of water, killing foreign divers, attaching mines to the hulls of foreign ships."
The dolphin facility in Crimea used to be under Ukrainian control, but was seized by the Russian navy in 2014, when Russian forces took over the peninsula.
Prof Rikardsen, who teaches at the University of Tromso, said "belugas, like dolphins and killer whales, are quite intelligent - they are Arctic animals and quite social, they can be trained like a dog".
He said the harness was difficult to remove - the last clip was undone by attaching a hook to it and letting the whale drag the Norwegian fishing boat.
"The beluga had come to the boats repeatedly for two or three days, looking for food, with its mouth open," he told the BBC.
"It's a challenge now if the whale will adjust to natural food. Also it needs to find a group - if not, it will probably still come up to a boat."
US Navy dolphins
During the Cold War the US Navy set up a special programme for training dolphins and sea lions in California.
The US Navy Marine Mammal Program, based in San Diego, uses bottlenose dolphins and California sea lions for locating mines and other dangerous objects on the ocean floor.
The navy website also says the animals are used to detect unauthorised personnel underwater who could potentially harm US ships.
The US Navy deployed dolphins to the Gulf during the Iraq War in 2003 to help mine-clearance teams.