Ukrainians have nowhere to retreat and will defend their homeland from Russian invaders, Kyiv mayor and former heavyweight boxing champion Vitali Klitschko said from the capital city on Thursday.

Flanked by his heavyweight boxing star brother Wladimir, Vitali Klitschko spoke via Skype as Russia's invasion of Ukraine entered its second week. Moscow was shelling several Ukrainian cities as its main assault force remained at a halt north of Kyiv.

"Thousands, already tens of thousands are killed in this war against Ukraine. And this number will unfortunately only grow," Vitali said from a shelter he is working from in Kyiv.