By Denis Sinyakov

MALAYA VISHERA, Russia, Aug 14 (Reuters) - A Russian express train heading from Moscow to St Petersburg was derailed late on Monday after the driver heard a loud bang under the wheels, overturning carriages and wounding dozens of passengers.

Russian Railways said in a statement it was the result of "unauthorised interference in the functioning of the train".

"There was a bang under the train. Unfortunately that is the only way we can describe it until investigators and the FSB (state security service) ... reach their own conclusions," Sergei Mikhailov, an aide to Russian Railways chief Vladimir Yakunin, told Vesti-24 television station.

The train derailed just after crossing a bridge over a road, said a Reuters photographer at the scene.

A conductor on the train showed Reuters a video he recorded on his mobile telephone of a crater about 2 metres (6 ft) across that could be seen on the bridge where the rails should have been.

"We felt the brakes come on sharply after the bridge, after that the train shook. A panic started," one conductor, who did not want to be identified, told Reuters.

"We smashed out the glass and helped the passengers out ... The worst damage was in the restaurant car. That is where most of the casualties were."

Viktor Beltsov, a spokesman for Russia's Emergencies Ministry, said 27 injured people were admitted to hospital. "Three are in a serious condition," he said.

No one was killed. Russian news agencies said 60 people were hurt but most did not need hospital treatment.

CARRIAGES ON THEIR SIDE

The Reuters photographer said nearly all of the carriages and the locomotive were off their tracks, while at least three carriages were tipped onto their side.

Powerful lights had been set up at the trackside as FSB investigators inspected the site and railway workers with cutting equipment removed damaged rails.

The derailment occurred in the Novgorod region, about 500 km (300 miles) north of Moscow, near the village of Malaya Vishera. The line between Moscow and Russia's second city of St Petersburg is among the country's busiest.

"As a result of an explosion at 21:38 (1738 GMT) ... several carriages of passenger train No. 166 from Moscow to St Petersburg were derailed," Russian Railways said in its initial statement.

Russia has a history of violent attacks on civilian targets, many carried out by groups linked to a separatist insurgency in the southern Chechnya region.

But no major attacks have been launched outside Chechnya and neighbouring regions for at least a year after many insurgents were either killed or arrested.

Nearly 250 passengers and crew were on board the train when it came off the rails. Those who were not injured were transferred to another train bound for St Petersburg.

The derailed train was blocking two sets of tracks, causing delays to other rail traffic. (Additional reporting by Guy Faulconbridge, Olga Petrova and Denis Pinchuk)

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