Head of Stockholm's International Peace Institute (SIPRI) Dan Smith says Russia's use of nuclear weapons would inflict "unprecedented damage at a global scale," after Russian President Vladimir Putin ordered Russia's nuclear forces be put on high alert. Moscow has the world's largest arsenal of nuclear weapons and a huge cache of ballistic missiles which form the backbone of the country's deterrence forces. Russia's invasion of Ukraine, now in its eighth day, has driven one million Ukrainians from their homes and plunged Russia into deepening isolation as a global pariah in the worlds of finance, diplomacy and sports. IMAGES AND SOUNDBITES