Vitali Klitschko and his brother Vladimir, former world heavyweight boxing champions, visited a front-line military checkpoint on the outskirts of the Ukrainian capital, Kyiv, on Sunday.

Pictures spread of Vitaly, who is also the mayor of the Ukrainian capital, Kiev, and his brother during their visit to the checkpoint, wearing bulletproof vests.

The front-line tour comes as Russian forces advance into the capital with the aim of besieging it, after spotting a 40-mile-long convoy bound for Kyiv this week.

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A post shared by Віталій Кличко (@vitaliyklitschko)

The mayor of Kyiv said that Russian forces were ignoring the new ceasefire, stressing that heavy fighting was continuing around his city.

Vitali Klitschko, 50, praised the patriotism of Ukrainians, saying to CNN, "I am very proud to see how patriotic people are. We are not interested in how strong the Russian army is, we are ready to fight. We are ready to die for our homeland and our families." .

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A post shared by Віталій Кличко (@vitaliyklitschko)

He added, "Our future is...and there are those who want to come to our house and steal our future from us."

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A post shared by Wladimir Klitschko (@klitschko)

In a previous interview, the two former heavyweight champions confirmed that they "have already killed 6 people in the capital, as Ukrainian forces are trying to eliminate separate Russian groups."

This comes days after Vitaly warned that Russia risks a "Chernobyl/Fukushima combined" if it continues to attack Ukraine's nuclear power plants.