Russia launched a nighttime attack on Ukraine’s power grid that President Volodymyr Zelenskyy said involved more than 300 drones and ballistic and cruise missiles. Zelenskyy said the strikes underscored Moscow’s lack of any public sign that it was willing to end the invasion of its neighbor anytime soon.

Zelenskyy said the attack knocked out heating to more than 5,600 apartment buildings in Kyiv, according to the city’s mayor, Vitali Klitschko. Klitschko added that nearly 80% of the affected buildings had recently had their heating supply restored after a major Russian barrage on Jan. 9, which plunged thousands of residents into a dayslong blackout.

Ukrainian officials said the renewed strikes were part of a broader escalation against the electricity supply. The cold-weather setting in Kyiv was emphasized in the reporting, with temperatures falling to minus 20 C (minus 4 F).

At the same time, Ukrainian officials sought to preserve momentum in U.S.-led peace efforts. The reporting said a Ukrainian negotiating team arrived in the United States on Saturday, and that its main task was to convey how Russian strikes are undermining diplomacy, as Zelenskyy described.

Zelenskyy said last week the delegation would also try to finalize with U.S. officials documents for a proposed peace settlement, related to postwar security guarantees and economic recovery. He said that if American officials approved the proposals, the U.S. and Ukraine could sign the documents at the World Economic Forum in Davos, Switzerland, this week.

The reporting also described how Russian officials planned for engagement at Davos. Kremlin spokesman Dmitry Peskov said Tuesday that presidential envoy Kirill Dmitriev plans to meet with some American representatives at Davos, while refusing to name the officials involved. The report said media coverage indicated the meeting could include U.S. envoy Steve Witkoff and Jared Kushner, Trump’s son-in-law.

Ukraine’s top diplomats and international rights officials condemned the strikes. Foreign Minister Andrii Sybiha said Ukraine needs urgent assistance and additional sanctions on Russia to make Moscow change course. On X, Sybiha wrote that Vladimir Putin’s “barbaric strike this morning is a wake-up call to world leaders gathering in Davos,” and the reporting said he directed the message to leaders assembled in Switzerland.

In Geneva, U.N. Human Rights Chief Volker Türk said the repeated strikes on Ukraine’s energy infrastructure “can only be described as cruel,” adding that they “must stop.” Türk also said that targeting civilians and civilian infrastructure is a clear breach of the rules of warfare, according to the report.

The reporting said several electrical substations providing power vital for nuclear safety in Ukraine were affected, citing Rafael Mariano Grossi, director-general of the International Atomic Energy Agency.

Ukraine’s air defense response was described through figures provided by its air force command. The report said Ukraine shot down or jammed 27 missiles and 315 drones, while five missiles and 24 drones hit 11 locations.

Ukraine’s leadership and the report also said air defenses are under strain and costly to sustain. Zelenskyy said some air defense systems recently ran out of ammunition before a new shipment arrived, and he said the air defense ammunition used against the missiles overnight cost about 80 million euros (about $93 million), according to the reporting.

The report added that Zelenskyy said Ukraine’s air defenses were adopting a new approach, including the appointment of Pavlo Yelizarov as a new deputy air force commander. Zelenskyy said late Monday that the system would be transformed, while providing no further details.