KYIV, Ukraine — Russian airstrikes targeted Ukraine’s energy facilities again Thursday as the first snow of the season fell in Kyiv, a harbinger of the hardship to come if Moscow’s missiles continue to take out power and gas plants as winter descends.

Separately, the United Nations announced the extension of a deal to ensure exports of grain and fertilizers from Ukraine that were disrupted by the war. The deal was set to expire soon, renewing fears of a global food crisis if exports were blocked from one of the world’s largest grain producers.

Even as all sides agreed to extend the deal, air-raid sirens sounded across Ukraine on Thursday. At least four people were killed and more than two dozen wounded in the drone and missile strikes, including one that hit a residential building, authorities said.

The Kremlin’s forces have suffered a series of setbacks on the ground, the latest being the loss of the southern city of Kherson. In the face of those defeats, Russia has increasingly resorted to aerial onslaughts aimed at energy infrastructure and other civilian targets in parts of Ukraine it doesn’t hold.

Thursday’s salvo appeared to be on a lesser scale than the nationwide barrage of more than 100 missiles and drones that knocked out power to 10 million people earlier this week. Those strikes Tuesday were described by Ukraine’s energy minister as the biggest barrage yet of the nearly 9-month-old invasion against the battered power grid.

That bombardment also resulted in a missile landing in Poland, killing two people. Authorities are still trying to ascertain where that missile came from, with early indications pointing to a Ukrainian air-defense system meant to counter the Russian barrage.

Polish President Andrzej Duda on Thursday visited the site where the mis- sile landed and expressed understanding of Ukraine’s plight. “It is a hugely difficult situation for them and there are great emotions. There is also great stress,” Duda said.

The renewed strikes come as many Ukrainians grapple with the discomforts of regular blackouts and heating outages as winter approaches. A light snow dusted the Ukrainian capital on Thursday, where the temperature fell below freezing. Kyiv’s military administration said air defenses shot down at least two cruise missiles and five Iranian-made exploding drones.

In eastern Ukraine, Russia “launched a massive attack on gas production infrastructure,” Oleksiy Chernyshov, head of the state energy company Naftogaz, said in a statement. He gave no details.

Russian strikes also hit the central city of Dnipro and southern Ukraine’s Odesa region for the first time in weeks. And critical infrastructure was hit in the northeastern region of Kharkiv, in the area of Izyum, wounding three workers, the regional administration said.

The head of Ukraine’s presidential office, Andriy Yermak, called the strikes on energy targets “naive tactics of cowardly losers” in a post Thursday on the messaging app Telegram.

“Ukraine has already withstood extremely difficult strikes by the enemy, which did not lead to results the Russian cowards hoped for,” Yermak wrote.

Ukrainian President Volodymyr Zelensky posted on Telegram a video that he said was of one of the blasts in Dnipro. The video from a vehicle dash-cam shows a fiery blast engulfing a rainy road.

“This is another confirmation from Dnipro of how terrorists want peace,” Zelensky wrote, referring to the Kremlin’s forces. “The peaceful city and people’s wish to live their accustomed lives. Going to work, to their affairs. A rocket attack!”

Valentyn Reznichenko, governor of the eastern region of Dnipropetrovsk, said a large fire erupted in Dnipro after the strikes hit an industrial target. The attack wounded at least 23 people, Reznichenko said.

Russia’s Defense Ministry said its strikes in Dnipropetrovsk hit a factory that produces military rocket engines.

An infrastructure target was hit in the Odesa region, Gov. Maksym Marchenko said on Telegram, warning of the threat of a “massive missile barrage on the entire territory of Ukraine.”

Elsewhere, a Russian strike that hit a residential building killed at least four people overnight in Vilnia in the Zaporizhzhia region.