A train explosion inside Russia's longest tunnel, a major transportation link to China, is being called an act of sabotage by Russian authorities. Ukrainian security services said that explosives had been detonated in the tunnel because Russia had been getting war materials by that rail route from China. From Reuters' 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. [snip]
Preliminary findings suggested that explosives had been placed beneath the train, Kommersant cited a source as saying. There were no casualties. [snip]
Such an attack, more than 4,000 km (2,500 miles) from Ukraine, illustrates Kyiv's readiness to conduct sabotage deep inside Russia." (our emphasis)
That's a big feat and demonstrates how serious and committed Ukraine is to taking the war deep inside enemy territory, and in a highly efficient way to disrupt supplies headed for the front. The more these acts succeed, the more the Russian population may question the war effort and the Putin regime.
