President Volodymyr Zelenskiy said the drone and missile barrage in the early hours of Sunday killed four people and caused damage across the north, south and east of the country, including the cities of Zaporizhzhia, Kryvyi Rih and Odesa, as well as in the Sumy and Chernihiv regions.
"Such killings now, when real diplomacy could have already begun long ago, are a deliberate crime and a prolongation of the war," Zelenskiy said in a post on social media platform X, issuing a fresh appeal to allies to strengthen Ukrainian air defences.
Just after sunrise, thick smoke could be seen rising into the clear blue sky from the burning top floor of the main government building, located in the historic Pecherskyi district, Reuters witnesses said.
Elsewhere in Kyiv, residential apartments were hit and damaged, with dozens of residents wrapped in blankets gathering on the streets outside to survey the damage to their homes as rescue workers fought to extinguish the flames.
US President Donald Trump said he is ready to move to a second phase of sanctioning Russia, the closest he has come to suggesting he is on the verge of ramping up sanctions against Moscow or its oil buyers over the war in Ukraine.
Until now, Trump, who met Putin last month, has resisted imposing tougher sanctions on Russia.
US envoy to Ukraine Keith Kellogg said the Russian attack looks like an escalation in the conflict.
"The attack was not a signal that Russia wants to diplomatically end this war," Kellogg wrote on X.
US Treasury Secretary Scott Bessent said additional economic pressure by the United States and Europe could prompt Russian President Vladimir Putin to enter peace talks with Ukraine.
Zelenskiy said he spoke with French President Emmanuel Macron, co-ordinating diplomatic efforts, next steps and contacts with partners.
Kyiv's European allies have condemned the attack and vowed to stand by Ukraine politically and militarily, but concrete offers of assistance, including the possibility of troops on the ground, are still being discussed.
Ukrainian Prime Minister Yulia Svyrydenko said it was the first time in the war the main government building in Kyiv had been hit, a symbolic blow to a well-defended part of the city.
Polish Prime Minister Donald Tusk said on X the Russian attack on Kyiv's government showed "again that the continued delaying (of) a strong reaction against Putin and the attempts to appease him made no sense".
Russia launched 805 drones against Ukraine overnight and 13 missiles, with Ukrainian air defence units downing 751 drones and four missiles, the air force said.
That was the highest number of drones Russia has used to attack the country since Moscow launched its full-scale invasion in February 2022.
Russia's defence ministry said it had carried out strikes on Ukraine's military-industrial complex and transport infrastructure, according to the Tass news agency. Both sides deny targeting civilians.
Timur Tkachenko, head of Kyiv's military administration, said an infant's body was pulled from the rubble in the Darnytskyi district, where a four-storey apartment building was damaged.
A young woman was also killed in the attack on the district, which lies to the east of the Dnipro River, he said. The interior ministry said more than 20 people were wounded in the capital. Air alerts lasted for more than 11 hours in Kyiv and the surrounding region.
