Russian officials say a bomb explosion derailed an express passenger train late Friday, killing at least 26 people and injuring more than 50 others.

Russian news media quote Russia's railways chief, Vladimir Yakunin, as saying a second smaller device exploded near the crash site Saturday, about 400 kilometers northwest of Moscow. 

Russian investigators earlier said they found elements of a home-made explosive device at the crash site near the town of Bologoye in the Tver region.

Prosecutors say a criminal investigation is under way that could result in terrorism charges, but they have not identified suspects.

The Nevski Express high-speed luxury train was traveling between Moscow and St. Petersburg when it derailed.  A small crater was found at the site of the wreck.   

The train was carrying more than 650 passengers and at least 20 crew members.

News reports from Russia quote witnesses as saying they heard an explosion before the train abruptly stopped, causing four carriages to derail.  Two carriages were overturned. 

The injured were taken to two area hospitals.

Russian President Dmitri Medvedev Saturday hosted a conference on the train crash and observed a minute of silence for the victims. 

The White House released a statement, saying it is deeply saddened by the terrible loss of life and injuries.