What sank the Russian sub?

Above water: the Kursk at dock before its sinking

LONDON (CNN) -- Russian authorities are continuing to offer competing theories to explain why the nuclear powered submarine Kursk sank.

Five days after the accident, the navy announced new evidence indicating a massive explosion had shattered large areas of the vessel, while the Defence Minister said a collision appeared to be the cause.

The government had initially blamed a collision between the Kursk and another vessel, but that was played down after mini-submarines circled the crippled craft and found evidence of extensive damage to the submarine's front section.

Explosion theory 1 Torpedo explodes 2 This triggers further blast 3 Escape capsule damaged 4 Air generators destroyed 5 Sub sinks in seconds

But Russian Defence Minister Igor Sergeyev said on Thursday that the collision theory appeared more and more credible.

The head of a government investigating commission, Vice Premier Ilya Klebanov, was due in the rescue area on Thursday to continue the search for answers.

Rescuers shot new video of the submarine on the bottom of the Barents Sea for five hours on Wednesday and that videotape will be analysed by Klebanov's commission.

A submersible rescue vessel, which is attempting to make contact with the Kursk's 118 sailors, discovered significant damage to the nose of the submarine, while the periscope was extended.

Navy officials said they believe the latest evidence suggested the vessel crashed to the seabed in seconds following an explosion in the torpedo compartment.

Navy spokesman Captain Igor Dygalo said: "The accident happened so quickly we can say it was like a flash." The damage apparently included the submarine's internal escape capsule located in the conning tower, making it impossible for the submarine's sailors to leave, Dygalo said. Air generators may have been destroyed instantly.

A likely scenario was that one torpedo exploded, setting off a much bigger explosion in the compartment that is packed with torpedoes, the officials said.

U.S. submarines monitoring Russian navy exercises when the Kursk was lost detected two explosions at the time.

The second explosion was much larger than the first, Russian press reports said.

UK officials -- basing their findings on the Russian navy's videotape of the accident site -- said on Thursday that the submarine had suffered "extensive damage" from a high energy source.

The Kursk can carry up to 28 torpedoes and anti-submarine missiles, each with warheads weighing up to 1,000 pounds.

An explosion involving even a few torpedoes would have caused catastrophic damage, navy officers said.

The Russian navy had been firing dozens of missiles and bombs in the area as part of training exercises and there was no evidence the explosion heard by the U.S. submarine was linked to the Kursk.

The Defence Minister's revival of the collision theory contrasted with the information provided by the naval officials.

The United States has denied any of its submarines or ships collided with the Kursk.

Criticism has been mounting over a lack of reliable information on rescue efforts and conflicting accounts of what went wrong.

Analysts told the Associated Press (AP) news agency the navy's behaviour was a throwback to the Cold War era with a free-for-all of officials announcing dubious, poorly informed theories.

"Sometimes they're lying, sometimes they don't know what's happening," Vladimir Urban, deputy editor of the Military News Agency and a former naval officer, said.

One factor likely to be examined during the accident investigation is the declining standards and resources of the Russian Navy.

During the past decade, the navy decommissioned hundreds of ships because it could not afford repairs and maintenance.

It has mostly sent its ships on short training runs near their bases due to the lack of funds to buy fuel.

The AP reported that the navy keeps only three nuclear submarines on patrol at any given time out of a force that numbered more than 100 vessels a decade ago.

Earlier theories to explain the Kursk's sinking have now been discounted.

They included the flooding of the submarine's torpedo tubes following the firing of a weapon and collision with an iceberg.

The Associated Press & Reuters contributed to this report.

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