Former world heavyweight champion boxer Wladimir Klitschko has announced that he has joined Ukraine's reserve army as the country prepares itself for a potential invasion by Russia.

Russia has sent more than 100,000 of its troops on the Ukrainian border, with many nations worldwide fearing that the forces could soon be deployed in an invasion.

While Russia denies those claims, the country has said that it could take military action unless its security demands are met, after opposing Ukraine's decision to join the US-led NATO military alliance.

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And Klitschko, who amassed 64 wins and five losses during his impressive boxing career, is now ready to do everything it takes to help defend his country.

Speaking at the opening of Ukraine's first ever territorial defense forces recruitment centre in Kyiv, Klitschko said: "When seeing my country is geopolitically struggling, so I am right here. I can't stand still – and I won't. That's why I am here.

"I signed up as a reserve for the territorial forces, for defending the city of Kyiv, because of everything that is currently going on around Ukraine and the aggression from the Russian side. For weeks if not months, there have been reports on how serious this is.

"One district from here, my little girl is going to school. The school is currently closed because the ambassadors have sent the families home. 

"It is the love, the love for my city, my home, my family, my neighbors, my daughter that has brought me here today, that I took this initiative and am now taking part in this territorial defense."

Meanwhile, his brother Vitali Klitschko, who also holds an impressive record as a professional boxer before retiring from the sport to become a politician, stood alongside Wladimir at the opening of the center on Wednesday.

Vitali said he was hopeful that an agreement can be reached between Russia and Ukraine without the need for combat, but he warned that they are prepared to fight if necessary.

"Before our enemies make an attack against Ukraine, they have to sink. We're strong, this will be a very painful price for everyone," he said.

"We hope our diplomats, Ukrainian diplomats, will give all knowledge to stop this aggression in a diplomatic way. If not, we have to prepare to take weapons in our hands, and defend the country."