Wladimir Klitschko has pleaded with the rest of the world to 'act now' before it becomes too late to halt the Russian invasion of Ukraine.
On Tuesday, President Vladimir Putin directed the deployment of Russian troops into their neighbouring country on what he labelled a "peacekeeping mission," sparking Ukrainian civilians to flee the border into Poland.
Former two-time world heavyweight boxing champion Klitschko, and brother Vitali, have joined the hundreds to have voluntarily offered to defend the country as soldiers.
But with the death toll rising and the collateral damage to houses and other buildings escalating, Wladimir, 45, has now issued a strong warning over the perceived 'catastrophe' ahead if other nations don't step up to help.
Via his Twitter account, on Saturday he posted a video message - with a sternly worded order attached.
"I'm Wladimir Klitschko and I am addressing the entire world to stop this war that Russia has started," he said.
"Just today civilians were shot with the rockets, with special operations and civilians getting killed and it's happening in the heart of Europe.
"There is no time to wait because it's going to lead into a humanitarian catastrophe.
"You need to act now to stop Russian aggression with anything you can have now."
And the 1996 Olympic gold medalist was adamant there was no time to lose.
"In an hour, or by tomorrow, it's going to be too late. Please get into action now, don't wait. Act now. Stop this war."
His post was accompanied with a series of meaningful hash tags, which read "#StayWithUkraine, #Ukraine, #StayTogether, #StandTogether, #Demo4Democracy, #United, #StopRussia, and #StopTheWar."
Klitschko has been active on Twitter ever since the harrowing conflict began, posting yesterday "There is no democracy without democrats. Get involved and use the freedoms that democracy offers you to express your support and solidarity."
He's also frequently retweeted footage of anti-war protests and posts condemning Russia's actions.
Vitali, 50, who has served as the mayor of Ukraine's capital Kyiv since 2014, said there was no alternative for him but to join arms.
He told ITV's Good Morning Britain this week: "I don’t have another choice, I have to do that. I’ll be fighting."
