Sobolev is an businessman from Donetsk, a flashpoint of pro-Russian insurgency in Ukraine.

Ukraine and Western governments accuse Moscow of sending weapons and troops to support a pro-Russian insurgency in eastern Ukraine.

Ukraine has also erected border fences since Russia's 2014 annexation of Crimea and the pro-Russian insurgency in eastern Ukraine.

A prominent militant who backed the pro-Russian insurgency in eastern Ukraine has been shot dead in a restaurant in an exclusive suburb of Moscow.