Military equipment has been pictured in a convoy as it appears to be heading to the frontline by a train connected to a Russian defence division that handles nuclear weapons.
Vladimir Putin has indicated that he is prepared to use nuclear weapons to defend Russia and the tension has been ramped up by his annexation of four regions of Ukraine where heavy fighting is taking place.
The fear is that he could claim an attack on these areas in the east and south of Ukraine would be an assault on Russian territory and so pave the way to using nuclear weapons.
