Investigators and rescue workers are seen Saturday amid wreckage and damaged coaches at the site of a train derailment near the town of Uglovka, some 250 miles northeast of Moscow. Russian officials said the incident was an act of terrorism.

Uglovka, Russia ? A powerful homemade bomb sent a high-speed Moscow-to-St. Petersburg train careening off its tracks, Russian officials said Saturday, killing at least 26 people in what officials consider an act of terrorism.

The head of Russia’s Federal Security Service, Alexander Bortnikov, said experts found pieces of an explosive device that detonated around 9:30 Friday night as the train raced over it, gouging a five-foot crater and strewing smoking wreckage over a rural stretch of track. He said a terrorism inquiry had been opened.

As many as 100 people were left injured by the disaster, officials said, and 18 remained missing Saturday night.

“Indeed, this was a terrorist attack,” said Vladimir Markin, a spokesman for the investigative committee of Russia’s General Prosecutor’s Office, according to Interfax. Bortnikov said the bomb exploded with a force equivalent to 15 pounds of TNT.

The attack on the Nevsky Express, a luxury train popular with government officials, tourists and business executives, was Russia’s deadliest terrorist strike outside the volatile North Caucasus region since 2004.

Among the dead were citizens of Belgium, Italy and Azerbaijan, Governor Valentina Matvienko of St. Petersburg told the state-run RIA Novosti news agency.

The force of the derailment scattered battered carriages over a remote stretch of track, trapping some of the injured for hours. By first light Saturday, luggage and pieces of metal lay in the muddy embankment in the drizzle, as survivors huddled under blankets by fires.

A second explosive device partially detonated at the crash site later Saturday as railway workers tried to clear the debris, said Russian Railways chief Vladimir Yakunin.

The initial blast derailed the last three carriages of the 14-car Nevsky Express as it approached speeds of 130 mph, officials said. More than 650 passengers and crew were aboard at the time.

The crash occurred near the border of the Novgorod and Tver provinces, some 250 miles northwest of Moscow and 150 miles southeast of St. Petersburg.

As rescue workers searched for victims, officials provided sometimes conflicting numbers for the dead and injured.

Health Minister Tatyana Golikova said at least 26 people were killed, 18 were missing and nearly 100 injured in the derailment. The Prosecutor General’s office said the death toll had risen to 30, with 60 others in the hospital.

As of Saturday evening, there were no credible claims of responsibility. But sketches were being composed of several suspects, Interior Ministry chief Rashid Nurgaliyev told Interfax, including a man of about 40 with red hair.

Witnesses said the train left the tracks after a loud explosion.