MOSCOW?(UPDATE 4) Thirty-nine people were killed in the overnight derailment of a Russian passenger train, the ITAR-TASS and Interfax news agencies reported on Saturday, citing emergency officials.

"In all there are 39," Alexander Basulin, an official at Russia's emergency situations ministry, was quoted as saying by ITAR-TASS. "There were 25 at the beginning, and 14 more were found outside the carriage."

Separately, Interfax quoted an unnamed rescue worker as saying that the death toll had risen to 39 from the previous reported figure of 25 while 87 were reported injured.

The passenger train derailed late Friday evening in Russia's Novgorod region as it traveled between Moscow and Saint Petersburg.

Russian television showed footage of the mangled wreckage of four overturned wagons of the Nevski Express, which officials said came off the tracks late on Friday evening in the Novgorod region.

An unnamed security official was quoted by the Interfax as saying that a one meter-diameter (three-foot wide) crater was found near the scene of the disaster.

"Witnesses say they heard a loud bang before the accident. This could be proof of an attack," the source said.

The crater could have been caused by an "explosion from a device placed underneath one of the wagons," Ria-Novosti quoted another security official as saying.

A railway official also told Itar-Tass that "an attack is one of the possibilities" being looked at by the police.

"That version must be carefully studied by law enforcement authorities," Alexander Pirkov, an advisor to the president of the Russian railway company, was quoted as saying by Interfax.

Four wagons of the 14-carriage train, carrying around 660 passengers, derailed at 9:34 p.m. (1834 GMT), according to the emergencies ministry.

Emergency services rushed to the scene of the crash, and by 0100 GMT all the injured had been evacuated to local hospitals, Russia media reported.

Several medical teams and a mobile hospital were also dispatched to the area.

Rescue work continued through the night, with fears four to six people might still be trapped underneath the wreckage of the overturned wagons, said Itar-Tass.

"Two wagons were completely overturned ... Several people were completely crushed under the metal. I heard screams, moaning," said, Andrei Abramenko, a police officer who happened to be traveling on the train, on Vesti 24 television.

The station showed footage of rescuers working among the wreckage under powerful searchlights.

In August 2007, a bomb on the same line derailed a train, injuring 60 passengers, with Chechen separatist or ultra-nationalist groups suspected.

Russian President Dmitry Medvedev ordered the head of the FSB domestic security service, Alexander Bortnikov, and Prosecutor General Yuri Chaika to lead the investigation into the causes of the derailment, the Kremlin said in a statement.

The country's anti-terrorism committee dispatched units to the area to help with the rescue effort and the investigation, Interfax reported.

Shoigu held a crisis meeting in Moscow with Interior Minister Rashid Nurgaliyev and Health Minister Tatiana Golikova, and was expected to visit the scene of derailment Saturday morning, the news agency reported.

In Washington, the White House said it was "deeply saddened by the terrible loss of life and injuries" from the railway accident, spokesman Robert Gibbs said in a statement.