Ukraine probes claims poisonous substance was dropped in Mariupol

Residents stand outside their apartments as shops burn after a Russian attack in Kharkiv, Ukraine (AP)

Ukrainian officials are investigating a claim that a poisonous substance was dropped on besieged Mariupol, as Western officials warned that any use of chemical weapons by Russia would be a serious escalation of the already devastating war.

Thwarted in his apparent ambition to overrun the Ukrainian capital Kyiv, Russian President Vladimir Putin is now building up forces for a new offensive in the eastern Donbas region, and insisted that his campaign would continue until it achieves its goals.