An unidentified explosive device detonated early on Monday under a freight train in the Russian North Caucasus republic of Dagestan, no one was killed or injured, police said, RIA Novosti reported.
"The explosion resounded under the train's locomotive. The train did not derail," a police spokesman said, adding that some passenger trains could be delayed over the incident.
Attacks on police and officials are frequent in Russia's volatile North Caucasus republics.