The beluga whale Hvaldimir, first spotted four years ago wearing an unusual harness and cameras on its head, leading to suspicions it was being used for espionage by the Russian navy, is currently off the west coast of Sweden, according to an NGO tracking its movements.

The whale was first spotted in 2019 in the waters of the Norwegian Arctic, and the name they gave it then is a combination of the Norwegian word "hval", which means whale, and the second part of the common Russian name Vladimir.

After being spotted in Oslo Fjord in recent days, it was spotted further south in the North Sea on Sunday at Hannebostrand on Sweden's west coast, he told AFP. Sebastian Strand, a biologist from the OneWhale organization.

He added that Hvaldimir had been swimming south for an unknown reason in recent months, after spending three years off the northern coast of Norway, which is part of his natural habitat.

"We don't know why it's been moving so fast lately," especially because it's "moving away from its natural habitat," Strand said.

"It could be hormones that prompt him to find a mate." Or maybe loneliness. "We know that belugas are very social, maybe he is looking for other members of his species," he adds.

According to experts, Hvaldimir is between 13 and 14 years old. It was spotted in April 2019 near the Arctic region of Finnmark, in the far north of Norway.

He gained notoriety because he had a special headband with two GoPro camera mounts on it that said "St. Petersburg equipment," leading some experts to assume he belonged to the Russian army, possibly using it for espionage. Biologists successfully removed his belt.

At the time, the Norwegian Fisheries Authority speculated that Hvaldimir had escaped from the enclosure and was being trained by the Russian navy. It seemed to be used to human company and approached ships without fear.

Moscow has never officially commented on these speculations.