Tensions between Moscow and Kiev have reached boiling point over recent months. In September, Ukrainian President Volodymyr Zelenskiy warned an all-out war with Russia could be a “possibility”.
Speaking at the Yalta European Strategy (YES) summit, Mr Zelenskiy said: “I think there can be.
“It’s the worst thing that could happen, but unfortunately there is that possibility.”
Sergei Ryabkov, Russia’s deputy foreign minister, warned that, if tensions between Moscow and Ukraine continue to rise, there could be a repeat of the Cuban missile crisis.
He said: “You know, it really could come to that.
“If things continue as they are, it is entirely possible by the logic of events to suddenly wake up and see yourself in something similar.”
Now, thousands of Ukrainians have joined the nation’s Territorial Defence Forces (TDF), a voluntary section of the army.
Pictures show civilians taking part in military training sessions outside Lviv on Tuesday.
One woman, Mariana Zhaglo, said she is willing to do whatever it takes to defend her country.
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She continued: “I have never hunted in my life.
“I bought this carbine after listening to some soldiers discussing the best rifle to get.”
French President Emmanuel Macron became the latest Western leader to vow to retaliation if Russia proceeds with an invasion.
He said: “If there is an attack, there will be retaliation and the price (for Russia) will be very high.”
Earlier this month, Moscow accused Ukraine of moving heavy artillery towards the front line of fighting with pro-Russian separatists and failing to engage in a peace process.
Kiev denied Russian accusations that it plans to seize back territory by force and Mr Zelenskiy said in December he was hopeful of reaching a new ceasefire deal.
Russian President Vladimir Putin said talk of an invasion is “provocative” and accused Ukraine and NATO of fanning tensions.
Valery Gerasimov, head of the Russian armed forces, was quoted by Russian news agencies as telling foreign military attachments the situation in eastern Ukraine was escalating and Kiev was to blame.
He said: “Deliveries of helicopters, unmanned aerial vehicles and airplanes to Ukraine are pushing the Ukrainian authorities to take sharp and dangerous steps.
“Any provocations of the Ukrainian authorities by way of a forced settlement of the problems of Donbass will be suppressed.”