World heavyweight boxing champion Wladimir Klitschko has lashed out at Russian president Vladimir Putin, saying his actions in eastern Ukraine could set off a third World War.

The 38-year-old Ukrainian says the war makes no sense as Ukraine and Russia are like brothers.

Klitschko has also called on western countries to be more forceful in dealing with Russia.

He says in boxing they have a saying be aggressive towards the aggressor and he believes Putin won't stop if they don't show him where the limits are.

Wladimir Klitschko's older brother Vitali entered politics after a successful boxing career and is currently mayor of Kiev.