KYIV, Ukraine — Ukrainian authorities said Sunday that two airstrikes a day earlier had killed at least 18 civilians, one of the highest single-day tolls so far this year and a grim reminder of the war’s enduring devastation as it approaches its fourth year.

The first strike occurred Saturday morning when a Russian missile hit a residential building in the Ukrainian city of Poltava, nearly 150 miles from the front lines, killing at least 14 people, including two children, according to local emergency services. Videos from the aftermath of the attack showed a section of the building reduced to rubble, with clothes and documents scattered across the area.

A few hours later, Ukrainian authorities said that a Russian bomb had smashed into a boarding school in Sudzha, a town in western Russia that is under Ukrainian control, killing four people.

The Russian Defense Ministry blamed Kyiv for the deadly strike in Sudzha and did not address the attack on Poltava. Neither side’s claims could be independently verified.

— The New York Times