Chechen rebels claimed responsibility Wednesday for last week's Russian train bombing, which killed at least 26 people and injured scores of others, a Web site sympathetic to the militants said. The claim, posted on the Kavkazcenter.com site, could buttress the suspicions of officials who are tracing the attack to Islamist separatists in Russia's North Caucasus region. It also raises fears of a fresh wave of attacks outside the region after a five-year break - a renewal of violence that would mirror the growing unrest inside the region. The separatist statement, issued on behalf of Chechen separatist leader Doku Umarov, claimed Friday's bombing of a Moscow-St. Petersburg express train was carried out on his orders. "We declare that this operation was prepared and carried out ... pursuant to the order of the Emir of Caucasus Emirate," or Umarov, the statement said. Umarov is thought to head a network of separatist cells across Russia's volatile and mainly Muslim North Caucasus region that are fighting to break free from Moscow's rule. The rebels are blamed for regular attacks on law enforcement officials in the region's five autonomous republics, after two bloody separatist wars in Chechnya. Russian authorities have said the train's derailment was an act of terrorism and traces of explosives and a crater were found at the disaster site. Government officials were among those killed in the train bombing. If confirmed, the bombing would mark the first deadly terrorist attack outside the North Caucasus since the bombings of two airliners and a Moscow subway station attack in 2004. Rights activists charge that devastating militant attacks in the Caucasus - such as August's bombing of a police station in the capital of Ingushetia, which claimed more than 20 lives - are the bitter fruit of a brutal counterterrorism campaign. The past year has seen a surge in suicide bombings and assassinations. "The scariest thing is that this might not be an isolated attack," said political analyst Yulia Latynina in an online commentary. "It could be the start of a series." At the same time, rights activists say, government security services in the region have increased the use of kidnappings, killings and home-burnings of suspected militants and their relatives. The Moscow-based rights group Memorial issued a report this month accusing authorities of implementing "a policy of state terror." The government has denied wrongdoing, blaming the separatists for trying to turn locals against Moscow. There has been no official accusation of the southern separatists, but the country's top investigator, Alexander Bastrykin, said in comments published Wednesday in the state newspaper Rossiiskaya Gazeta that the attack bore their hallmarks. Police released a computerized sketch of a suspect Monday. Bastrykin's office said Tuesday that he had been injured when a second blast struck the scene of the bombing as sappers and rescue workers were sifting through the wreckage. Russian news agencies said the injury was not serious. No arrests have been made in connection with the attack on the luxury Nevsky Express, which occurred 250 miles (400 kilometers) northwest of Moscow and 150 miles (250 kilometers) southeast of St. Petersburg. It was the second attack in two years on the line, which is popular with civil servants and businessmen. A blast in 2007 injured dozens but killed no one. Two arrests were made in connection with that attack but the main suspect, former military officer Pavel Kosolapov, remains a fugitive. Russian media reports have quoted officials as saying the same group could be behind both bombings.