Equipped with a nuclear reactor and two nuclear warheads, the Komsomolets submersible caught fire in April 1989 as a result of a short circuit while in international waters 500 kilometres (310 miles) from Norway.

Its crew was unable to put out the fire, leaving the nuclear vessel to sink and killing 42 people in one of the world's worst submarine disasters.

The wreckage has since been kept under close monitoring, with Russian investigators reporting in the early 1990s and 2007 that it was leaking radiation.

A joint Russian-Norwegian expedition in 2019 found the submarine was leaking radiation up to 800,000 times above normal levels, though Norway said the pollution had little impact on its fish and seafood.

In a statement Wednesday, the Roshydromet environmental monitoring agency said a new expedition had departed a day earlier from the city of Arkhangelsk in Russia's northwest carrying a group of scientists.

"The main goal of the expedition is to collect data on the state of the marine environment to assess the possible consequences of its contamination with radioactive products from the nuclear submarine," Roshydromet said.

The environment monitor said the team will take samples of water, seabed sediment and radioactive aerosols near the carcass of the damaged submarine, which sits at a depth of 1,027 metres (3,370 feet).

The expedition will return to Arkhangelsk on June 5.

At the time, the Komsomolets accident raised fears of another Chernobyl, after an explosion at a nuclear reactor in the ex-Soviet Ukraine city caused the world's worst nuclear accident three years earlier.

Russia has also seen nuclear accidents in recent years.

A month after the joint Russian-Norwegian expedition examined Komsomolets in 2019, a blast at a missile test site near Arkhangelsk killed five people and caused a spike in radiation levels.