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.

Air assaults on Saturday killed at least four people. Kharkiv’s mayor described an overnight strike as “the most powerful attack” since the beginning of the war.

Russia struck Ukraine with a thunderous aerial bombardment overnight, further dampening hopes that the warring sides could reach a peace deal anytime soon.

A planned exchange of Russian and Ukrainian prisoners of war failed to take place on Saturday, with Moscow accusing Kyiv of postponing the swap at the last minute, which Ukrainian officials dismissed as more “dirty games” from the Kremlin.

China said on Saturday it was willing to accelerate the examination and approval of rare earth exports to European Union firms.

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

Ukraine’s security service released footage Wednesday of its attack on Russian war planes at multiple airbases across the country. In the span of a few hours on Sunday, nearly a third of Moscow’s strategic bomber fleet was destroyed or damaged with cheaply made drones sneaked into Russian territory, according to Ukrainian officials.

Russia's claims that Ukraine is delaying exchange of soldiers' bodies are untrue, Ukrainian officials said on Saturday, urging Moscow to stop "playing dirty games" and return to constructive work.Kremlin aide Vladimir Medinsky said on Saturday that Ukraine had unexpectedly postponed exchanging prisoners of war and accepting the bodies of killed soldiers for an indefinite period.