Russia on Tuesday announced the start of tactical nuclear weapons drills close to Ukraine, in what it said was a response to Western "threats". Throughout its two-year offensive on Ukraine, Moscow has repeatedly talked-up its arsenal of nuclear weapons and its readiness to deploy them if it senses an existential threat. The West has accused President Vladimir Putin of irresponsible nuclear sabre-rattling. Russia's defence ministry said Tuesday the drills were taking place in its Southern Military District, which borders and includes parts of Ukraine that Moscow claims to have annexed. It did not specify exactly where.