Russia's top investigator was injured by a bomb that went off as he and colleagues scoured the wreckage of a passenger train derailed by an earlier explosion, his office said Tuesday.

The last three carriages of the Nevsky Express flew off the tracks late Friday, killing at least 26 and injuring dozens more in what officials consider a terrorist bombing.

Another bomb exploded Saturday as investigators and rescue workers scoured the wreckage, Russian Railways said, giving no word on injuries.

On Tuesday, however, the federal Investigative Committee under the Prosecutor General's Office said its chief Alexander Bastrykin had been hurt by the bomb, which was detonated by remote control. Russian news agencies reported the injury was not serious.

"This gives the investigation grounds to believe that the second blast — could have been directed against investigators," the statement said.

No arrests have been made in connection with the derailment, which occurred some 250 miles northwest of Moscow and 150 miles southeast of St. Petersburg. Police on Monday released a computerized sketch of a possible suspect.

The Investigative Committee cautiously added its backing Tuesday to the theory that terrorists from the volatile North Caucasus could be to blame. A railway official said Monday that the double-blast tactic — detonating a bomb in the vicinity of a blast site that officials had arrived to investigate — placed suspicion on Islamist separatists in Russia's south, who are thought to employ it frequently.

Meanwhile, the Emergency Situations Ministry said Tuesday that the death toll had risen to 27, Russian news agencies reported. There was no word from the Health Ministry on the figure it had been giving — 26. The ministries have given conflicting numbers throughout the derailment's aftermath.