Marina Eratova Pravda, February 20, 2001, p. 2
Duma Deputy Vice Admiral Valery Dorogin: The governmental commission believes that components of torpedo fuel must have blown up in the torpedo compartment. Temperature in the compartment soared and caused another explosion, and eventually fire.
Personally I think a foreign submarine must have been involved at least to some extent. Moreover, there is indirect evidence that this is precisely what happened.
This is how hypotheses of the catastrophe rate in a descending order in the opinion of the governmental commission: internal reasons (50% probability), collision with a foreign submarine (30%), and explosion of a floating mine, relic of World War II (20%).