A Russian missile and drone attack in the Ukrainian city of Kharkiv early Saturday killed at least three people and injured more than 20 others, officials have confirmed.

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.

Technological advances have given threadbare militaries and rebel fighters the ability to strike stunning blows against far stronger forces.