Ukraine probes claim poisonous substance dropped in Mariupol

Ukraine investigated a claim that a poisonous substance was dropped on besieged Mariupol, as Western officials warned Tuesday 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, Russian President Vladimir Putin is now building up forces for a new offensive in the eastern Donbas region, and insisted Tuesday that his campaign would achieve its goals. He said Russia “had no other choice” but to launch what he calls a “special military operation,”...