The attack on Friday, which killed at least four people in the capital, came two days after Russia vowed retaliation for an audacious Ukrainian drone assault.

President Trump said the Russian leader Vladimir Putin had warned that he would retaliate for a covert Ukrainian attack in Russia last weekend that destroyed dozens of Russian bombers.

Kyiv, Ukraine — Russia bombarded six regions of Ukraine in one of its largest aerial attacks of the three-year war, Ukrainian officials said Friday. The nighttime assault lasted for hours and killed three emergency responders in the capital Kyiv, according to authorities.