Tomorrow is too late: Boxing great Klitschko calls on world to 'stop Putin'

Former world boxing heavyweight champion Wladimir Klitschko appealed to the world on Saturday to stop the conflict in his native Ukraine and prevent a humanitarian catastrophe.

Wladimir and his brother Vitali, also a former world heavyweight champion and now mayor of Kyiv, have both vowed to take up arms against invading Russian forces.

"I'm addressing the entire world to stop this war that Russia has started," he said in a video posted online.

"There's 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. In an hour, or by tomorrow it's going to be too late."

Wladimir enlisted in Ukraine's reserve army earlier this month, saying at the time that his love for his country compelled him to defend it.

Russian forces invaded Ukraine from three sides early on Thursday in what President Vladimir Putin called a "special military operation" to protect people, including Russian citizens, subjected to "genocide" in Ukraine - an accusation Kyiv and the West calls baseless propaganda.