US President Donald Trump said he was prepared to move forward on new sanctions on Moscow, hours after Russia fired its biggest-ever aerial barrage at Ukraine.
Speaking outside the White House, he replied "yeah, I am" when asked if he was ready to impose more sanctions against Russia, without giving further details.
Ukrainian President Volodymyr Zelensky said he was counting on a strong US response to the latest barrage.
"We are counting on a strong response from America. That is what is needed," he said in his evening address.
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Russia launched its largest air attack of the war on Ukraine overnight, setting the main building of the Ukrainian government on fire in central Kyiv and killing at least two people in the capital including an infant, Ukrainian officials said.
Ukraine's President Volodymyr Zelensky said the drone and missile barrage also 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," Mr Zelensky 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 from the burning top floor of the main government building, located in the 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, meanwhile, has expressed growing frustration with Russia since he met Mr Putin last month, but has so far resisted imposing tougher sanctions on Russia as a way of bringing Moscow to the negotiating table.
On Friday, he said he was still working on security guarantees for Ukraine that he said would help bring an end to the deadliest conflict in Europe since World War II.
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.
War's biggest drone barrage
Ukrainian Prime Minister Yulia Svyrydenko said it was the first time in the war that the main government building in Kyiv was 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 claimed 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. Air alerts lasted for more than 11 hours in Kyiv and the surrounding region.
Earlier, Kyiv's Mayor Vitali Klitschko said an elderly woman died in a bomb shelter in Darnytskyi district, but the cause of her death was not immediately known.
He also said a pregnant woman was among those wounded.
In Kyiv's Sviatoshynskyi district in the west, several floors of a nine-storey residential building were partially destroyed, Mr Klitschko said.
Falling drone debris set off fires in a 16-storey apartment building and two more nine-storey buildings, he added.
Ukraine targets Russian energy
Ms Svyrydenko called for more weapons for Ukraine and for the world to respond to the Russian attacks.
"We will rebuild the buildings," Ms Svyrydenko said.
"But lost lives cannot be brought back. The enemy terrorises and kills our people across the country every day."
Ukraine's defence ministry said that a new meeting of Kyiv's allies was planned for next week and air defences and supplies for Ukraine's deep strikes on Russia would be discussed.
The military said it attacked the Druzhba oil pipeline in Russia's Bryansk region, inflicting "comprehensive fire damage" during an overnight attack.
It is part of a strategy to target Russia's vast energy complex, which is the financial backbone of its economy and helps fund the war.
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.
In the southern city of Odesa, civilian infrastructure and residential buildings were damaged, with fires breaking out in several apartment blocks, regional governor Oleh Kiper said.
Three people were wounded in the attacks, he said.
Read more: 'Coalition of the Possible'? How Ukraine's security guarantees might look
