Relatives identified loved ones killed in the wreck of the express train. If confirmed as caused by a bombing, the wreck would be Russia's deadliest terrorist attack outside the violence-plagued North Caucasus provinces in five years.
Television networks took entertainment programs off the air and moments of silence were observed before matches on the final Sunday of the Russian football league.
Patriarch Kirill, the leader of the country's dominant church, led a service for the victims at Christ the Savior Cathedral near the Kremlin. "We will remember their sacred names," he said.
"Our people have been challenged. A crime of which any one of us could have been a victim has been committed for effect," Kirill said in a statement on the church's Web site. "They want to frighten everybody who lives in Russia."
The rear three cars of the Nevsky Express, one of Russia's fastest trains, derailed on a remote stretch of track late Friday as it sped from Moscow to St. Petersburg, killing some passengers and trapping others in the jumbled wreckage. The head of Russia's Federal Security Service, Alexander Bortnikov, said Saturday that an explosive device detonated under the train, gouging a crater in the rail bed and blowing the tail cars off the tracks.
Emergency Situations Minister Sergei Shoigu said at least 25 people were killed and 26 were unaccounted for, though he said some may have survived uninjured or never have boarded the train. The ministry later said the number unaccounted for was down to 12.
Health Minister Tatyana Golikova said 85 people remained hospitalized, 21 in grave condition, according to Russian news agencies. A Belgian and an Italian were among those hurt.
Recovering from a broken rib at a hospital in St. Petersburg, Natalya Tarasova said she and her sister were reading in the third car from the rear when she heard a bang and felt the windows shake. The car swung wildly from side to side and she was thrown to the floor, her sister toppling onto her.
"People were tossed around the carriage like rags," said Tarasova, 36, who works in a jewelry business and was returning home after an exhibition in Moscow. "Suitcases were jumping from the racks like frogs and falling on people."
She said conductors collected medicine and other items from passengers and took the supplies to the two more badly damaged rear cars, which were left hundreds of meters back and were where most of the casualties occurred.
"It was scary, but there was no panic," she said.
Relatives were identifying victims Sunday at a hospital morgue in Tver, the closest sizable city to the wreck site near the border of the Tver and Novgorod provinces, about 250 miles (400 kilometers) northwest of Moscow.
The state-run railway company, Russian Railways, said train traffic was fully restored. There were no credible claims of responsibility or word on a possible motive.
Russia has been hit by a number of major terrorist attacks since the 1991 Soviet collapse, most linked to the 1990s wars between government forces and separatist rebels in Chechnya and the violence the conflicts have spawned across the surrounding North Caucasus.
Extreme nationalists were blamed for an explosion that caused a derailment along the same railway line in 2007, injuring 27 passengers. Authorities arrested two suspects in that blast and are searching for a third, a former military officer.