Russia launched a barrage of ballistic missiles and strike drones at Ukrainian cities in overnight attacks, Ukrainian officials said Thursday, while negotiations for another U.S.-brokered round of talks remained uncertain.

Ukrainian President Volodymyr Zelenskyy said late Wednesday that Washington had proposed further negotiations next week between Russian and Ukrainian delegations in either Miami or Abu Dhabi, where the last meeting took place. Zelenskyy said Ukraine “immediately confirmed” it would attend and that, as he understood it, Russia was “hesitating.”

Kremlin spokesman Dmitry Peskov said Thursday that another round of talks was expected “soon,” but he did not provide further details.

Alongside the diplomatic uncertainty, Russia continued striking civilian areas and infrastructure, Zelenskyy said. The Ukrainian president said Moscow had not responded to a U.S. proposal for an “energy ceasefire” that would also halt Ukrainian drone strikes on Russian oil facilities, and he said the United Nations human rights chief Volker Türk urged Russia to stop hitting electricity infrastructure, reminding Moscow that targeting civilian infrastructure is prohibited under international humanitarian law.

Zelenskyy said Russia fired 219 long-range strike drones, 24 ballistic missiles and a guided aircraft missile at Ukraine overnight from Wednesday into Thursday, according to Ukraine’s air force. The main targets, Ukraine’s air force said, included Kyiv, Kharkiv, Dnipro and the southern port city of Odesa—cities that have come under relentless bombardment.

In Dnipro, regional head Oleksandr Hanzha said Russian strikes injured four people, including a 4-year-old girl and a newborn boy. Kyiv’s city administration said several residential buildings were damaged and two people were injured, and in Odesa regional head Oleksandr Hanzha said one person was injured as a residential high-rise was partially destroyed and a market and a supermarket caught fire.

Ukraine’s officials also described fallout for heating and water services after the attacks. Oleksii Kuleba, deputy prime minister for the restoration of Ukraine, said the Kyiv attack left 2,600 buildings without heating, in addition to 1,100 buildings in the capital already without heating from previous attacks. Kuleba said nearly 300,000 residents in Odesa lost running water and that in Dnipro the central heating system stopped working for some 10,000 people, as temperatures were above freezing in Kyiv but remained bitterly cold.

Ukraine reported retaliatory strikes as well. Ukraine’s General Staff said a domestically developed long-range drone hit the Ukhta oil refinery in Russia’s Komi region, around 1,750 kilometers (1,000 miles) from the Ukrainian border. An official with Ukraine’s Security Service, known as the SBU, told The Associated Press it was the first time Ukrainian drones had flown that far, speaking on condition of anonymity because the official was not authorized to speak publicly.

Ukraine’s general staff also said one of its domestically produced long-range “Flamingo” missiles hit one of Russia’s biggest storage sites for missiles, ammunition and explosives in Russia’s Volgograd region and caused major explosions. Separately, Ukrainian forces hit and started a fire at the Michurinsk Progress Plant in Russia’s Tambov region, which Ukraine’s General Staff said is a defense enterprise producing high-technology equipment for aviation and missile systems.

In other developments, the White House said first lady Melania Trump helped reunite a small group of Russian and Ukrainian children with their families after they became separated by the invasion. The White House said five children—four boys and one girl, ages 4 to 15—were reunited with their families in Ukraine, while one child returned to its family in Russia, citing Maria Lvova-Belova, the Kremlin’s commissioner for children’s rights. Lvova-Belova is wanted for war crimes by the International Criminal Court for allegedly deporting children from Ukraine, and the White House said it was the third such family reunification involving the first lady.