World heavyweight champion Oleksandr Usyk insisted he has “absolutely no fear” after taking up arms in Kyiv to defend his native Ukraine against invading Russian forces.

Less than six months on from outpointing Britain’s Anthony Joshua to capture three of the four major titles in boxing’s blue riband division, Usyk, 35, has joined his country’s territorial defence battalion.

Speaking from a basement in the Ukrainian capital, Usyk admitted the rematch against Joshua – which was widely anticipated to go ahead at some point in the spring or early summer – was understandably far from his thoughts.

While Usyk admitted his bewilderment at an escalating situation that has shocked most of the rest of the world, the former undisputed world cruiserweight champion believes he is ready for whatever lies in front of him.

“Maybe, it will sound sentimental but my soul belongs to the Lord and my body and my honour belong to my country, to my family, so there is no fear, absolutely no fear,” the WBA, IBF and WBO heavyweight champion told CNN.

“There’s just bafflement – how could this be in the 21st Century?

“I really don’t know when I’m going to be stepping back in the ring. My country and my honour are more important to me than a championship belt.”

Usyk’s compatriot Vasyl Lomachenko, a three-weight world champion who was reportedly on the verge of agreeing a June showdown against WBA, IBF and WBO lightweight champion George Kambosos Jr, has enlisted in the military, too.

Meanwhile, Kyiv mayor Vitali Klitschko and his brother Wladimir – both former world heavyweight boxing champions – have appeared together calling for more support from allies to defend Ukraine.

Wladimir said there were “never enough” resources as the country’s infrastructure has been partially crippled by shelling during a “terrible advance” over the past few days.

The mayor and his brother thanked governments which had provided international help but said basic supplies like food and water were needed as well as more weapons.

In a joint interview on BBC News, Wladimir said: “It’s never enough. There’s huge demand because infrastructure is partially destroyed by the shelling that is happening all over the country in the different cities.

“It’s absolutely not enough and we definitely need to support and help – financial support, military equipment support, medical support.”

Vitali added: “Everyone has to be involved. It’s war not against Ukraine, it’s war against (all) civilians and it’s war against democracy. We need support – support from the whole world.”