An explosion that derailed a train in Russia's North Caucasus was being investigated as an act of terrorism, Russian media reported.
No one was injured Sunday morning when the explosion pushed the locomotive and eight carriages of the freight train off the tracks, the state-run RIA Novosti reported.
The agency cited a top security officer claiming that the bomb was the latest in a string of rebel attacks in Russia.
Sunday's bombing happened near the Inchkhe station just outside the city of Makhachkala.
It follows the March 29 attacks in Moscow, where two female suicide bombers killed at least 39 people and wounded more than 60 others.
There were more explosions last week in the region, killing 12 people and wounding 29, RIA Novosti said.
Chechen rebel leader Dokku Umarov claimed that he personally gave orders to attack the Moscow subway in a video released last week.