The air raid hit “critical infrastructure” in and around Kyiv, as well as private homes, Ukrainian authorities said.
Russia launched 23 self-exploding drones over Kyiv while the city slept, but Ukrainian forces shot down 18 of them, the city's administration said on Telegram.
At least some of them were Iranian made, according to the capital's military administration.
“The enemy is attacking the capital with 'Shahed' barrage ammunition,” the administration said on the Telegram messaging app.
No major casualties were reported from the attack, although the Ukrainian president’s office said the war had killed at least three civilians and wounded 11 elsewhere in the country between Sunday and Monday.
The drone barrage caused emergency power cuts in 11 central and eastern regions of the country, including the capital region, authorities said.
The attack came as British Prime Minister Rishi Sunak urged allies to “go after” Iran’s ability to supply weapons to Russia that are killing civilians.
Speaking at a summit in Riga, Latvia, Mr Sunak condemned Tehran, which has sent more than 500 kamikaze drones to Russia that have been used in deadly attacks on Ukraine’s people and energy supply.
“We must continue to focus on degrading Russia’s capability to regroup and to resupply and that means going after its supply chains and removing the international support,” he said.
“Particularly I’m thinking of Iran and the weapons that it is currently providing to Russia, which we should be very strong about calling out as we have done in the United Nations.”
Monday was St Nicholas Day, an occasion that marks the start of the Christmas holidays in Ukraine, when children typically receive their first gifts hidden under pillows.
“This is how Russians congratulated our children on the holiday,” Serhii Kruk, the head of Ukraine’s State Emergency Service, wrote on Telegram, attaching photos of firefighters barely distinguishable amid the flames at a building that had been attacked.
Mr Putin’s trip to Belarus on Monday afternoon, his first in three and a half years, has been described by the Kremlin as a broad “working visit” with Belarusian President Alexander Lukashenko.
The country allowed its territory to be used as a launch pad for Moscow's February 24 invasion of Ukraine, but has not joined the fighting directly.
Mr Lukashenko has said repeatedly he has no intention of sending his country's troops into Ukraine. And Russia has dismissed suggestions Mr Putin plans to pressure Belarus into joining the operation as “stupid and unfounded fabrications”.
Russian troops that were moved to Belarus in October will conduct battalion tactical exercises, the Interfax news agency reported, quoting Russia's Ministry of Defence.
It was not clear when and where in Belarus the latest in a flurry of recent exercises will be conducted.
Monday’s strikes against Kyiv came days after Russia launched one of its largest missile attacks against Ukraine, attacking the power grid on Friday.
Two people died in the barrage, which damaged nine energy facilities and forced Kyiv to introduce emergency power cuts across the country amid freezing temperatures.
Ukraine becomes dark patch in night satellite images — in pictures
Several explosions were heard on Monday, but it was not clear whether they were air defence systems destroying the drones or drones hitting buildings.
Emergency power cuts were reintroduced in Kyiv after the attacks, electricity provider Yasno said.
Ukrainian President Volodymyr Zelenskyy on Sunday again called for western nations to beef up the country's air defences.
The conflict has killed tens of thousands of people and driven millions from their homes.
Mr Zelenskyy told Ukrainians the armed forces were holding firm in the town of Bakhmut, the scene of the fiercest fighting in the country for many weeks, as Russia attempts to advance in eastern Ukraine's Donetsk region.
“The battlefield in Bakhmut is critical,” he said. “We control the town even though the occupiers are doing everything so that no undamaged wall will remain standing.”
Denis Pushilin, the Russian-installed administrator of the portion of the Donetsk region controlled by Moscow, said Ukrainian forces shelled a hospital in Donetsk city, killing one person and injuring several others.
Reuters could not independently verify the battlefield accounts.
Mr Putin cast Russia's “special military operation” as a watershed moment when Moscow finally stood up to a western bloc, led by the US, seeking to capitalise on the 1991 fall of the Soviet Union by destroying Russia.
Kyiv and the West said Mr Putin has no justification for what they have decried as an imperial-style war of occupation that has resulted in Russia now controlling about a fifth of Ukraine.
Henry Kissinger, an architect of the Cold War policy of detente towards the Soviet Union as US secretary of state in the 1970s, said the time was approaching for a negotiated peace.
Ukraine rejected the proposal, saying it amounted to appeasing the aggressor by sacrificing parts of the country.