A bomb derailed an elite passenger train speeding through the forest from Moscow to Saint Petersburg, killing up to 39 people and injuring nearly 100, Russian officials said Saturday.

"We are indeed talking about a terrorist attack," Vladimir Markin, spokesman for the federal investigative committee, was quoted as saying by Interfax news agency. The committee said it had found bomb fragments at the scene.

Mangled and overturned carriages were strewn across the tracks and down the railway embankment as scores of orange-vested rescue workers searched urgently for further victims that could be trapped under the wreckage. Related article: Mangled wreckage

The incident occurred late Friday in an area where the same train, the prestigious Nevsky Express, was derailed after a bomb under the track ripped out a portion of the rail in August 2007, injuring around 60 people.

Witnesses including passengers on the train and inhabitants living near the site said they heard a loud boom just before the train went off the rails, and police told AFP at the site there was a large crater under the track.

The investigative committee said in a statement that its experts had found "elements of an explosive device" at the scene of the disaster, a wooded expanse 400 kilometres (250 miles) northwest of Moscow near the village of Uglovka.

There was no immediate confirmed claim of responsibility for the attack.

Echo of Moscow radio reported that a hardline nationalist group calling itself Combat 18 had claimed the blast, but its source for that report was a blog entry from an anti-immigrant activist that could not be verified.

Russian President Dmitry Medvedev ordered several law enforcement agencies to investigate the train attack thoroughly and to assist people affected by it.

"Make sure there is no chaos, because the situation is already tense," Medvedev said in a video conference with Interior Minister Rashid Nurgaliyev shown on state television.

In a meeting later with a government commission created to manage the crisis, also shown on state television, Medvedev expressed condolences for families of the victims and stood for a moment of silence.

There were conflicting reports on the death toll, but Alexander Basulin, an official at the emergency situations ministry, was quoted by the ITAR-TASS news agency as saying "in all, there are 39" dead.

Basulin said this number comprised 25 victims found immediately and another 14 people discovered later, outside the train carriages.

Interfax, quoting an unnamed official, also put the death toll at 39.

In a statement, however, the emergency situations ministry said only 26 fatalities had been confirmed while 18 passengers were still unaccounted for. It added 96 people were injured.

The disaster struck the Nevsky Express, which is the fastest train between Moscow and Saint Petersburg and is popular among foreign tourists and Russians who commute between the two cities.

Andrei Abramenko, a police officer who happened to be travelling on the train, described a picture of human suffering.

"Two wagons were completely overturned.... Several people were completely crushed under the metal. I heard screams, moaning," Abramenko said on the Vesti-24 state television news channel.

Four wagons of the 14-carriage train, carrying around 660 passengers and nearly two dozen staff, derailed at 9:34 pm (1834 GMT), according to the emergencies ministry.

At least three foreigners were on the train, ITAR-TASS reported, citing a source at Russian Railways. Other reports said that one Italian and two Finns were among the passengers.

In Washington, the White House said it was "deeply saddened by the terrible loss of life and injuries" from the incident.

In Paris, French President Nicolas Sarkozy expressed his "profound sadness" over the derailment.

This video is from Al Jazeera, broadcast Saturday, Nov. 28, 2009.

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Photo sample credit: Associated Press.

With AFP.