President Volodymyr Zelenskiy said the drone and missile barrage 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 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.
The attack underlined growing pessimism in Ukraine and among allies that the war can be ended any time soon, with Russian President Vladimir Putin resisting calls for a ceasefire and emboldened by strengthening relations with China.
US President Donald Trump has expressed growing frustration with Moscow since he met Putin in August but has so far resisted imposing tougher sanctions on Russia.
Kyiv's European allies have 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.
Russia launched 805 drones against Ukraine overnight and 13 missiles, with Ukrainian defence units downing 751 drones and four missiles, the Ukrainian air force said.
That was the highest number of drones Russia has used to attack the country since Moscow launched its full-scale invasion of Ukraine 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 attacks on the capital.
Earlier on Sunday, Kyiv's Mayor Vitali Klitschko said an elderly woman died in a bomb shelter in Darnytskyi.
Svyrydenko called for more weapons for Ukraine and for the world to respond to the Russian attacks.
"We will rebuild the buildings, but lost lives cannot be brought back." Svyrydenko said.
Ukraine's defence ministry said a new meeting of Kyiv's allies was planned for next week and air defences and supplies for Kyiv's deep strikes on Russia would be discussed.
Ukraine's military said it attacked the Druzhba oil pipeline in Russia's Bryansk region, inflicting "comprehensive fire damage" during an overnight attack on Sunday.
Dozens of explosions also shook Ukraine's central city of Kremenchuk, cutting power to some residents and damaging a bridge across the Dnipro River, Mayor Vitalii Maletskyi said on Telegram.
Russian strikes on Kryvyi Rih, also in central Ukraine, targeted transport and urban infrastructure, city officials said, but no injuries were reported.
