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NAZRAN, Russia, Oct 24 (Reuters) - Russian forces detained two Muslim men in the southern republic of Ingushetia in connection with the August bombing of a train between Moscow and St. Petersburg, an interior ministry source said on Wednesday.

Investigators had previously said Russian nationalists were the most likely culprits in the Aug. 13 explosion that derailed the main passenger train between Russia's two largest cities. There were no fatalities in the blast.

The Ingush interior ministry source said the two suspects were brothers, describing them as rebels and adding that Russian security forces had immediately sent them to Moscow for further questioning.

Islamist militants have attacked targets outside the north Caucasus region -- bombing Moscow's metro, kidnapping hundreds of people at a theatre and blowing up two passenger planes -- but the intensity of attacks has dropped away since the death of rebel Chechen leader Shamil Basayev in 2006.

Russian forces have fought two wars against rebels in Chechnya since 1994 that have scarred the north Caucasus region and killed thousands of people.

Violence has spilt over into the neighbouring republics of Ingushetia and Dagestan. This year Russia tripled the size of its forces in Ingushetia, though bomb attacks, kidnappings and deaths continue on a nearly daily basis.

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