The mayor of Kiev, the former world heavyweight boxing champion Vitali Klitschko, knows a thing or two about fighting.

       But even he is daunted by a potential Russian invasion of Ukraine, the possibility of which has loomed large since Moscow massed tens of thousands of troops near the territory.

       The 45-year-old, who turned to politics full-time after his retirement from boxing in 2013, has become a central voice in the crisis, which currently shows no signs of abating.

       He has been mayor of the Ukrainian capital since 2014 and was a leading figure in the Euromaidan protests.

       Now centre stage in the current crisis, Mr Klitschko, the only heavyweight boxer in history to have reigned as world champion in three different decades, wants his country’s allies to supply it with weapons to offset the enormous military advantage Russia has over its neighbour.

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       The UK and the US are among the countries that have so far obliged, sending thousands of anti-tank missiles to Kyiv in recent days.

       However, Germany, where Mr Klitschko lived for two decades, has taken a different approach to the crisis.

       Christine Lambrech, its new defence minister, said Berlin will not send lethal weapons, as they could “fuel the situation”. Instead, her country has confirmed it will send 5,000 military helmets to Ukraine.

       Speaking to the German tabloid Bild this week, the Kyiv mayor said this constituted a “betrayal” of Ukraine.

       "What kind of support will Germany send next?" he asked. "Pillows?"

       "The behaviour of the German government leaves me speechless. The defence ministry apparently hasn’t realized that we are confronted with perfectly equipped Russian forces that can start another invasion of Ukraine at any time," he added.

       Mr Klitschko also took Berlin to task for not explicitly stating that it will halt the Nord Stream 2, a gas pipeline from Russia to Germany, if Moscow attacks Ukraine.

       In contrast, he has thanked the British government for its help.

       The former boxer, who was dubbed Dr Ironfist during his career, a nickname which blended his sports science doctorate with his fearsome reputation in the ring, hopes diplomacy will win out. However, he is under no illusion about the threat his country faces.

       “Mr. Putin’s idea is to rebuild a Soviet empire. We don’t want to go back to the USSR. We see our future as a democratic European country,” he told CNN earlier this month.

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       He also told the BBC Radio 4 that Ukraine has no option but to defend itself, if attacked by its neighbour.

       “If someone comes to Ukraine, we don’t have a choice... we have to fight for our country,” he said.