A statement on a Web site sympathetic to Chechen rebels says the militants have claimed responsibility for last week's Russian train bombing that killed at least 26 and injured scores of others.
The Kavkazcenter.com Web site posted Wednesday what it said was a letter written on behalf of Chechen separatist leader Doku Umarov.
The statement says that Friday's bombing of a Moscow-St.Petersburg express train was carried out on Umarov's orders.
Russian authorities have said that the train's derailment was an act of terrorism.
The country's top investigator said in comments published in a state newspaper Wednesday that the tactics used by attackers were reminiscent of those frequently employed in the volatile North Caucasus.