Former heavyweight boxing champion Wladimir Klitschko made a global call for action Saturday, urging the "entire world" to take immediate action to stop Russia’s attacks on Ukraine.

Klitschko, the brother of Kyiv Mayor Vitali Klitschko, made a stern plea on Instagram for the international community to stand up to Russian President Vladimir Putin to prevent what he says will inevitably become a humanitarian crisis.

KLITSCHKO BROTHERS, HALL OF FAME BOXERS, VOW TO DEFEND UKRAINE, SAY PUTIN WANTS TO 'RESTORE FALLEN EMPIRE’

"I am addressing the entire world to stop this war that Russia has started," his video began. "Just today civilians were shot by the rockets … civilians getting killed, and it’s happening in the heart of Europe. There is no time to wait because that’s going to lead [to a] humanitarian catastrophe."

Kyiv mayor Vitali Klitschko (left) and his brother and former Ukrainian boxer Wladimir Klitschko speak to the press during a visit to a volunteer recruitment center in Kiev Feb. 2, 2022. (Genya Savilov/AFP via Getty Images)

"You need to act now to stop Russian aggression with anything you can [give] now," he continued. "In an hour or by tomorrow is going to be too late. Please get into action now. Don’t wait. Act now. Stop this war."

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In a LinkedIn blog post Thursday, Klitschko accused Putin of wanting to destroy the Ukrainian way of life while saying the attacks against the Eastern European nation are the result of years of "weakness in Western democracies."

Wladimir Klitschko ahead of his fight against Anthony Joshua at Wembley Stadium, London. (Nick Potts/PA Images via Getty Images)

"Putin wants to call into question the geopolitical balance across the whole of Europe, he dreams of being the defender of the Slavic peoples wherever they live and he wants to restore a fallen empire whose demise he has never accepted," he said.

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Earlier this month, Klitschko enlisted in Ukraine’s reserve army, explaining that his love for his country compelled him to join.

Former Ukrainian boxer Wladimir Klitschko (right) greets a staff member after he registered as a volunteer during a visit to a volunteer recruitment center in Kiev Feb. 2, 2022. (Genya Savilov/AFP via Getty Images)

"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," he said at the time, via Reuters.

Fox News’ Louis Casiano contributed to this report.