KYIV, Ukraine (AP) — Russia unleashed a wave of attacks on Ukraine targeting airfields and fuel facilities in what appeared to be the next phase of an invasion that has been slowed by fierce resistance. The U.S. and EU responded with weapons and ammunition for the outnumbered Ukrainians and powerful sanctions intended to further isolate Moscow.

Huge explosions lit up the sky early Sunday south of the capital, Kyiv, where people hunkered down in homes, underground garages and subway stations in anticipation of a full-scale assault by Russian forces.

Flames billowed into the air before dawn from...