Underground shockwaves detected at the UK Government's seismic monitoring station, Blacknest, confirm the submarine was rocked by two explosions.
Experts believe the first, smaller blast may have been caused by the leak of hydrogen peroxide (HTP), a colourless, odourless liquid used to propel the Kursk's torpedoes.
A fireball spreading to the front compartment of the submarine could have detonated stacks of stored torpedoes, sparking the second, massive explosion that flooded the Kursk with water.
Secret documents
The evidence, revealed in the BBC Science TV programme Horizon, draws on secret government documents concerning a submarine accident off the coast of Portland on the southern coast of England in June 1955.
Thirteen men died when the submarine, the Sidon, was blown apart by an experimental torpedo containing HTP.
When they examined the wreck of the submarine, investigators discovered that inside the torpedo a stainless steel pipe containing HTP had burst.
An inquiry concluded that this was what had caused the accident, although the precise mechanism remained a mystery.
Nearly half a century later, the Kursk disaster prompted Maurice Stradling, a torpedo designer and former lecturer at the Royal Naval Engineering College in Plymouth, to look again at how HTP could have caused an explosion on the Sidon.
Simple error
Mr Stradling concluded that HTP splashing over reactive metals inside the torpedo created a gas that blew open the torpedo casing.
He believes there are similarities between the Kursk disaster and the sinking of the Sidon.
"If the torpedo was accidentally started then because the propellers were not in the water there would be nothing to control the speed of the engine," Mr Stradling told the BBC. "The engine would have over-revved and the HTP pipe would have burst... allowing HTP to spray into the inside of the torpedo hull...and the whole ghastly chain of events would be in place."
Nobody will know for sure unless remains of the submarine's front compartment are raised. Although the Russians are trying to lift the Kursk, they plan to leave the front of the submarine on the seabed.
And, although the Royal Navy stopped using HTP in its torpedoes after the Sidon sinking in 1955, the Russians still use it, unlike almost all other countries.
The Horizon Special: What Sank The Kursk? can be seen on BBC Two at 2100 BST on Wednesday, 8 August