A rare albino killer whale who scientists feared may have died has been spotted for the first time in four years.

The marine mammal, named Iceberg, had not been seen since Spring 2012.

Just one in 10,000 killer whales - also known as orcas - are completely white, and researchers were alarmed by Iceberg's long absence.

He was pictured off the coast of Russia's Kuril Islands by American researcher Erich Hoyt, from the Far East Russia Orca Project (FEROP).

Killer whale Iceberg was last seen four years ago, and marine researchers have been desperately trying to confirm whether he is still alive

Despite being an incredibly-rare all-white killer whale, Iceberg was around 16 when he first came to the attention of scientists.

Researchers from the universities of Moscow and St Petersburg first noticed him near the Commander Islands in the North Pacific in August 2010.

At the time he was living in a pod with 12 family members.

Just one in 10,000 killer whales are completely white, and Iceberg has been described as 'breathtakingly beautiful'

When Iceberg was first seen, Hoyt said: 'This is the first time we have ever seen an all-white, mature male orca.

'It is a breathtakingly beautiful animal.'

Scientists have been fascinated by Iceberg, and are keen to study his behaviour.

The dramatic sight of Iceberg's dorsal fin, which measures more than 6ft, has prompted excitement among scientists

Hoyt said after a sighting in 2012: 'Iceberg seems to be fully socialised; we know that these fish-eating orcas stay with their mothers for life, and as far as we can see he's right behind his mother with presumably his brothers next to him.'

The incredibly-rare albino killer whale's whereabouts had baffled scientists for four years before the latest sighting

And the scientist was keen to find out how the rare mammal was able to survice, Fox News reported.

Hoyt said: 'We want to find out a lot more about Iceberg.

'We would like to find out how he is able to survive as a white whale.'

American researcher Erich Hoyt has described Iceberg as 'breathtakingly beautiful'

Four years since he was last spotted, 22-year-old Iceberg was photographed by researchers close to the Kuril Islands in the West Pacific

When Iceberg was first seen, he was believed to be part of a pod of 12 orcas