More than 21,000 civilians there are feared dead. russia is intensifying rocket attacks in kharkiv. missile strikes have killed several people, injuring more than a dozen. buildings are up in flames. the war in ukraine is exacting a heavy toll on families. many still struggling to escape the fighting. james longman leads us off from dnipro, ukraine. reporter: tonight, ukrainian forces defiant, locked in a fierce battle. in what could be the last stand for control of the critical port city of mariupol. ukrainian troops rejecting a russian ultimatum to surrender. they re holding out in this massive steel plant filled with underground tunnels. ukrainian prime minister saying mariupol is besieged but not defeated. we will fight until the end in this war. reporter: mariupol is now a wasteland after weeks of russian bombing and street fighting. bodies lying in the streets.