KYIV - An operation conducted by the Security Service of Ukraine (SBU) detonated explosives on a railway line in Siberia that Russia uses for military supplies, a Ukrainian source told Reuters on Nov 30.

The source, who declined to be identified, said four explosive devices were detonated overnight as a cargo train was moving through the Severomuysky Tunnel in Buryatia region, which borders Mongolia.

Such an attack, more than 4,000km from Ukraine, would be a striking demonstration of Kyiv’s ability to conduct operations deep inside Russia, amid Russia’s invasion of its neighbour.

Reuters could not independently verify the account, or whether the rail route is used for military supplies.

Russian sources acknowledged that a train had caught fire in the area, but made no mention of explosives.

Russia’s Investigative Committee said in a statement that a train carrying fuel caught fire in the tunnel on Nov 29 night, that there had been no casualties and that a preliminary probe was under way to establish the cause.

Russian Railways, the state company which owns and operates the rail network, said the train was stopped when they noticed smoke coming from a tank containing diesel fuel.

In a statement online, it said rail traffic had been rerouted, slightly increasing journey time, but that transport had not been interrupted. REUTERS