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.

Ukraine said its “Operation Spiderweb” attacked Russian warplanes worth hundreds of millions of dollars, utilizing drones that each cost under $1,000 and were launched from wooden containers carried on trucks.

Satellite imagery of a Russian air base taken shortly after Ukraine carried out a drone attack shows several strategic bombers were destroyed.