Oleksandr Usyk has signalled his intention to defend his world heavyweight titles against Anthony Joshua by announcing he will begin preparations for their fight.

Usyk conclusively outpointed Joshua at Tottenham Hotspur Stadium last September to claim the WBA, IBF and WBO belts although the Briton immediately indicated he would activate a contractual rematch clause.

There has been uncertainty aboutt when the return bout would take place after Usyk last month went back to his native Ukraine to enlist in the military following Russia’s invasion of the country.

But Usyk said on Instagram on Friday: “I decided to start preparing for a rematch with Anthony Joshua, a large number of my friends support me, all the rest of the good and peace, thank God for everything.”

The 35-year-old posted a video alongside the short message behind a building which bore a banner featuring the Ukrainian flag’s colours, with a message reading: “Hands off Ukraine, Putin!”

Usyk’s announcement paves the way for a summer showdown against Joshua, whose promoter Eddie Hearn earlier this week floated the idea of his fighter taking on someone else in an interim contest in June.

As a father of three young children, Usyk is exempt from the law that has required men of fighting age to stay in Ukraine and there are reports he has already departed the country.

Usyk, a former undisputed world cruiserweight champion, joined the territorial defence battalion in Kyiv last month and expressed bewilderment at the situation.

“There is no fear, absolutely no fear,” he 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 on the verge of agreeing a June showdown against WBA, IBF and WBO lightweight champion George Kambosos Jr, has also taken up arms.

Kyiv mayor Vitali Klitschko and his brother Wladimir – both former world heavyweight boxing champions – both remain in the Ukrainian capital and have been prominent voices against the Russian invasion.