Cities across western Russia have come under regular attack from drones since May, with Russian officials blaming Kyiv. Ukrainian officials never acknowledge responsibility for attacks on Russian territory or the Crimean peninsula. However, larger aerial strikes against Russia have previously followed heavy assaults on Ukrainian cities.

Russian drone strikes against Ukraine continued Saturday, with the General Staff of the Ukrainian Armed Forces reporting that 10 Iranian-made Shahed drones had been shot down across the Kherson, Khmelnytskyi, and Mykolaiv regions.

On Friday, Moscow’s forces launched 122 missiles and dozens of drones across Ukraine, an onslaught described by one air force official as the biggest aerial barrage of the war.

As well as the 39 deaths, at least 160 people were wounded and an unknown number were buried under rubble in the assault, which damaged a maternity hospital, apartment blocks, and schools.

Western officials and analysts recently warned that Russia limited its cruise missile strikes for months in an apparent effort to build up stockpiles for massive strikes during the winter, hoping to break the Ukrainians’ spirit.

Fighting along the front line is largely bogged down by winter weather after Ukraine’s summer counteroffensive failed to make a significant breakthrough along the roughly 620-mile line of contact.

Russia’s ongoing aerial attacks have also sparked concern for Ukraine’s neighbors.

Poland’s defense forces said Friday that an unknown object had entered the country’s airspace before vanishing off radars, and that all indications pointed to it being a Russian missile.

Speaking to Russian state media outlet RIA Novosti Saturday, Russia’s Charge d’Affaires in Poland, Andrei Ordash, said that Moscow would not comment on the event until Warsaw had given the Kremlin evidence of an airspace violation.

“We will not give any explanations until we are presented with concrete evidence because these accusations are unsubstantiated,” he said.