MOSCOW - At least 39 people were killed and 87 more injured when a Russian express train came off the rails late on Friday in what the national railway company said could have been a bomb attack.

The Nevsky Express, carrying 661 passengers from Moscow to St Petersburg, was derailed at 9:34 p.m. (1834 GMT) near the town of Bologoye, 350 km (200 miles) north of Moscow.

Russian television showed grainy footage of rescue workers working under flood lights near debris on the side of the train tracks.

"There are 25 dead and 87 injured," Emergencies Minister Sergei Shoigu told a heated video conference during which he barked out orders to local rescuers in the early hours of Saturday morning.

He said the fate of 41 other people was still unclear.

A spokesman for Russia's main domestic intelligence service, the FSB, declined to comment on whether an attack was suspected but Russian Railways said that an explosive device may have caused the derailment.

"One of the versions is that the cause of the incident was an explosive blast," the state owned train operator said in a statement. Interfax news agency said a one-metre (3-ft) wide crater had been found next to the railway track.

The derailment was Russia's worst train accident for years and talk of sabotage is likely to raise fears of an upsurge in attacks on the Russian heartland by rebels from the North Caucasus.

In 2007, 30 people were injured when a train operating on the same line was derailed after an explosion damaged rails. The men accused of the 2007 attack are suspected of having links to Chechen rebels.

President Dmitry Medvedev has been informed about the incident and Russian Railways chief Vladimir Yakunin was at the scene.

In Washington, White House spokesman Robert Gibbs said, "We are deeply saddened by the terrible loss of life and injuries resulting from the reported derailment of a train between Moscow and Saint Petersburg."

Russian transport officials said trains were being diverted along alternate lines on one of the country's busiest routes.