Western powers have strongly criticised Russian president Vladimir Putin after he called up military reserves to fight in Ukraine and threatened to use nuclear weapons to defend his country in what they dismissed as a sign of weakness amid defeats on the battlefield. Mr Putin portrayed his invasion of Ukraine as a fight for Russia’s survival against a hostile West, and backed forthcoming “referendums” in Russian-occupied parts of Ukraine that would pave the way for Moscow to annex some 90,000sq km of territory – an area bigger than the island of Ireland. In a clear escalation of his war on...