Russia bombarded Ukraine’s second-largest city with massive strikes in the early hours of Saturday, its mayor said, one night after Moscow carried out one of the war’s largest aerial assaults on Ukraine.

Former Rep. Chris Stewart, a former fighter pilot, says the U.S. isn’t prepared for this change in modern warfare.

Air defense crews in the capital were racing to combat a large-scale bombardment before dawn on Friday, officials said.

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.

President Trump said he discussed Ukraine's recent attacks on Russian bombers with Putin, adding that he's not optimistic about "immediate peace."