Russia's prosecutor-general, Vladimir Ustinov, said an investigation had established that an exploding fuel from a blank torpedo caused the other blasts that destroyed the submarine.

Ustinov said the blast was triggered by a complex chemical reaction

Speaking at a press conference in Moscow, Mr Ustinov said no one was to blame for the disaster, and no criminal charges would be filed.

Correspondents say the Russian government had long been reluctant to admit that its state-of-the-art submarine was destroyed by an internal malfunction.

Investigators had examined a number of other theories as to why the submarine sank in the Barents Sea in August 2000.

'Minute-by-minute account'

There were suggestions that the Kursk was struck by a torpedo from a foreign submarine or had hit a World War II mine.

But earlier this month, a Russian commission said an explosion of fuel in an old torpedo sunk the submarine.

This was confirmed on Friday by Mr Ustinov, who had been ordered by President Vladimir Putin to inform the public of a 100-page final report of the investigation.

Giving a minute-by-minute account of the investigation's report, Mr Ustinov said the Kursk was sunk by the blast in its own torpedo, which did not even have a warhead.

Russia was criticised for failing to accept offers of foreign help promptly

He said the volatile substance - hydrogen peroxide - used as its fuel in the torpedo exploded because of a complex chemical reaction.

"The initial impulse which triggered an explosion of the torpedo was the result of an unusual process of events inside the oxidising agent reserve of the torpedo," Mr Ustinov said.

This triggered a massive explosion of other, combat-ready torpedoes, and just over a minute after the initial blast the front section of the submarine was completely destroyed.

The prosecutor-general said that 23 mariners survived the initial explosion and gathered in the stern of the submarine.

He said they all died within six to eight hours, succumbing to carbon monoxide poisoning from the fires and high pressure.

After the disaster, the Russian Navy ordered torpedoes of that type that exploded to be removed from service.

No charges

Mr Ustinov said that the investigation had revealed some violations by Navy officials during the training exercises in the Barents Sea.

But he said he would not press criminal charges because the violations did not directly lead to the Kursk's demise or the death of the crew.

Three top Russian Navy officers were demoted and another eight sacked after failed rescue operation, which some experts said was a punishment for the Kursk disaster.

At the time, the Russian Government was criticised for not accepting offers of Western aid promptly.