Russian prosecutors say they are treating a train accident as an act of terrorism, after a Moscow to St Petersburg express is derailed after a crude bomb explodes on the track. Russia launched a terrorism investigation on Tuesday (August 14) after a bomb derailed an express train between Moscow and St Petersburg, overturning carriages and injuring dozens of passengers, officials said. In a meeting in Moscow the head of Russia's Federal Security Service (FSB) linked the attack late on Monday (August 13) to an insurgency in the south of Russia around Chechnya, where Moscow has been fighting a long rebellion against its rule. Russia President Vladimir Putin, on a visit to the Russian republic of Tuva, spoke to Transport Minister Igor Levitin, asking Levitin to keep him informed about the ongoing investigation. "Cooperate with the Health Ministry, the Ministry of Emergencies, and law-keeping organs to do everything in order to help people." Putin said to Levitin via telephone. " Everything that has not yet been done. Do everything to restore transport services. And a little later, give me an update on the situation. Liaise with the law-keeping forces, they already started a criminal investigation, and also with the FSB. Help them organise their operations." he added. But Interfax news agency quoted an unnamed investigator as saying the home-made bomb was similar to one used by two Russian nationalists to blow up a train near Moscow two years ago. Sixty passengers and train crew were hurt in the derailment near the village of Malaya Vishera, about 500 km (300 miles) north of Moscow and 170 km from St Petersburg, a Russian Railways spokeswoman said. About 250 people had been on board. The derailed train was an overnight service travelling on one of the country's busiest rail routes, heavily used by businesspeople and foreign tourists. The bomb was planted on a bridge over a road and left a crater about 2 metres (6 ft) across, witnesses said. "The train accident was caused by a home-made explosive device," Sergei Bednichenko, chief prosecutor for Russia's North West district, told Channel One television. "A criminal case has been opened under article 205, clause 3, that is terrorism." The train came off the tracks just after crossing the bridge and and at least three carriages were tipped onto their side, a Reuters photographer at the scene said. "There were two explosions which derailed the locomotive and a carriage in the middle." said Andrey, a steward on the train. "There is a crater about one metre across and destroyed rail out there." Viktor Korsakov, a spokesman for the regional Moscow-St. Petersburg railways confirmed that the crash was being investigated by the FSB. "The investigation on what caused the crash is underway, but it is the task for FSB." Korsakov said, "I can say that it was the result of unauthorised interference in the functioning of the train. There was a bang and what happened after nobody knows." Interfax quoted an FSB official as saying the bomb contained 2 kg (4.4 lb) of explosive material. FSB chief Nikolai Patrushev said it was part of a pattern of violence that included a spate of attacks on security forces and officials in the North Caucasus region around Chechnya. But one unnamed investigator told Interfax that wires found near the blast area, and possibly used to activate the explosive device, resembled those found in June 2005 when a train from the Chechen capital Grozny was blown up near Moscow. The two Russian nationalists charged with the 2005 blast were sentenced to 18 years in prison. Rebel fighters linked to Chechnya have also used bombs to target passenger trains in the past. Chechnya's separatist rebels have been weakened by the killing of many of their field commanders. They have not carried out any major attacks outside the North Caucasus for at least a year. But insurgent groups from neighbouring Russian regions -- most of them Islamist militants -- have been increasingly active, ambushing police patrols and bombing army bases.