Russian President Vladimir Putin told President Donald Trump in a phone call Wednesday that he was obligated to respond to Ukraine’s weekend drone attack, Trump said, setting up a potential escalation in the conflict just as the US president hopes to broker an end to the war.

At least five people, including a one-year-old child, were killed in a Russian drone strike on the northern Ukrainian city of Pryluky overnight, regional governor Viacheslav Chaus said Thursday.