Soviet-era submarines dumped more than 30 years ago in the Arctic Ocean are threatening a major nuclear catastrophe, according to a report by a German magazine.

The experimental sub K27 was sunk at a depth of just 33 metres, 100 times less than international guidelines.

Some scientists claim the vessel, which was deliberately sunk in the Kara Sea, is already leaking radioactive material.

“A creeping catastrophe has already begun. The longer these submarines are under water the greater the danger that more and more radioactivity will escape and contaminate the sea all around it,” said German nuclear security expert Wolfgang Renneberg .

An even bigger danger is the highly enriched nuclear fuel in its reactor, say scientists.

In August, Russia released details of 19 subs, 14 nuclear reactors and thousands of other pieces of radioactive waste lying at the bottom of the ocean.

As well as key fishing grounds, the Kara Sea is thought to hold more than 37 billion barrels of oil.

Experts from Russia and Norway are studying how to safely raise the K-27 from the seabed.