Satellite images of Russian air bases released Wednesday appear to show the aftermath of what Ukraine called "Operation Spider's Web."

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.

Ukraine unleashed more than a hundred drones smuggled deep into Russia in what it called its most damaging attack yet.

Russian drones struck apartment buildings in Ukraine's second-largest city, Kharkiv, triggering fires and injuring at least nine people, the city's mayor said early on Thursday.

The audacious attacks on Russian airfields highlight the power of unconventional, asymmetric warfare — and the threat to U.S. strategic bases and ports, experts say.

President Trump said Russian President Vladimir Putin told him he would have to respond to Ukraine’s recent attack, dampening the prospects for immediate peace between Moscow and Kyiv.

"It was a good conversation, but not a conversation that will lead to immediate Peace," President Trump posted on social media.

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