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 others 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. Tuesday’s strikes were described by Ukraine’s energy minister as the biggest barrage yet of the nearly 9-month-old invasion against the battered power grid.

It 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 bombardment.

Poland’s President Andrzej Duda on Thursday visited the site where the missile landed and expressed understanding for 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 bombings come as many Ukrainians are coping with the discomforts of regular blackouts and heating outages, as winter approaches. A light snow dusted the capital Thursday, where the temperature fell below freezing.

The city’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,” state energy company Naftogaz head Oleksiy Chernishov said in a statement. He provided no details.

Russian strikes also hit the central city of Dnipro and Ukraine’s southern Odesa region for the first time in weeks. And critical infrastructure was also 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 Telegram post on Thursday.

“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 Zelenskyy posted on Telegram a video that he said was one of the blasts in Dnipro. The footage from a vehicle dashcam showed a fiery blast engulfing a rainy road.

“This is another confirmation from Dnipro of how terrorists want peace,” Zelenskyy 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 Dnipropetrovsk region, said a large fire erupted in Dnipro after the strikes on the city 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.

In the Odesa region, an infrastructure target was hit, Gov. Maksym Marchenko said on Telegram, warning about 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 southern region of Zaporizhzhia. Rescuers combed the rubble for any other victims, according to Kyrylo Tymoshenko, a senior official in the Ukrainian presidential office.

Officials in the Poltava, Kharkiv, Khmelnytskyi and Rivne regions urged residents to stay in bomb shelters.

The war’s impact has been felt far beyond Ukraine, perhaps most significantly in global food markets. Ukraine and Russia are among the world’s largest exporters of grain, and Russia is also a significant producer of fertilizer.

There were concerns in recent days about the fate of a U.N.- and Turkey-brokered deal meant to address disruptions to those exports that was set to expire Saturday. U.N. Secretary-General António Guterres confirmed it had been extended for four months.

In addition to securing the safe passage of Ukrainian exports, Guterres said in a statement the United Nations is also “fully committed” to removing obstacles that have impeded the export of food and fertilizer from Russia.

The Russian Foreign Ministry confirmed the extension, and Zelenskyy called it a “key decision in the global fight against the food crisis.”