Investigators find train in Russian tunnel was blown up in 'terrorist act': Report

Investigators have concluded that a train that caught fire in Russia's longest tunnel on Wednesday was blown up in a "terrorist act" by unidentified individuals, the Kommersant newspaper reported on Friday.

A Ukrainian source told Reuters on Thursday that the Security Service of Ukraine (SBU) had detonated explosives in the rail tunnel in Siberia because Russia had been using the route for military supplies.

Kommersant cited unnamed sources as saying a criminal probe had been opened over the incident, which affected a cargo train moving through the Severomuysky tunnel in the Buryatia region, bordering Mongolia.

At 9.5 miles (15.3 km) long, the tunnel on the Baikal-Amur Mainline railway is Russia's longest, excluding urban underground railway tunnels.

Preliminary findings suggested that explosives had been placed beneath the train, Kommersant cited a source as saying. There were no casualties.

As Moscow's war in Ukraine grinds on, Kyiv is trying to disrupt the Russian war machine after its own counteroffensive achieved only modest gains and it now finds itself on the defensive in some places.

Such an attack, more than 4,000 km (2,500 miles) from Ukraine, illustrates Kyiv's readiness to conduct sabotage deep inside Russia.

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

Russian Railways had said the train was stopped when smoke was spotted coming from a tank containing diesel fuel.

It said rail traffic had been rerouted, slightly increasing journey time, but that transport had not been interrupted.

Moscow calls its Ukraine campaign a "special military operation".