The attacks came 10 months into President Vladimir Putin's invasion of Ukraine, with Russian strikes targeting the energy grid, leaving millions in the cold in the middle of winter.

Ukraine's air force said on Friday morning that Russia's overnight assault was made with "Iranian-made kamikaze drones".

A total of 16 drones were launched from the southeastern and northern directions and they were "all" destroyed by Ukraine's air defence, it said.

The presidency said Ukraine "withstood" the new drone attacks, which targeted infrastructure.

In the capital Kyiv, city authorities announced an air alert shortly after 2:00 am local time.

Mayor Vitali Klitschko later said seven drones had targeted the capital. Two were shot down "on approach" and five over the city.

There were no casualties, but falling debris damaged windows in two buildings in southwestern Kyiv, he added.

One of the drones hit a four-storey administrative building, starting a fire that was later extinguished, said Kyrylo Tymoshenko, deputy head of the presidential office.

- Barrage of missiles -

The drone attack came after a barrage of Russian missiles battered Ukraine on Thursday morning, with blasts reported across the vast country, from the northeastern city of Kharkiv to Lviv in the west near the Polish border.

Ukraine's army said Russia had launched several dozen cruise missiles, the majority of which had been shot down.

Russia's defence ministry said Friday it had carried out a "massive strike" the day earlier on military command and energy facilities.

"All assigned targets were reached," according to the ministry.

Tymoshenko said four civilians were killed and eight received injuries on Thursday.

On Friday, three people were killed by Russian shelling, he said.

Ukrainian President Volodymyr Zelensky said most regions were left without power following Thursday's attack.

Ukraine's energy operator said Friday the damage had a "much smaller impact" on the power grid than "the enemy expected" and the power deficit was back to the levels before Thursday's attack.

But "the situation in the southern and eastern regions is still difficult," Ukrenergo added.

Russia has faced international condemnation and an onslaught of unprecedented sanctions over its war in Ukraine.

The growing international isolation has forced Putin to seek closer political and economic cooperation with nations in the Middle East, Africa and Asia.

- Putin speaks to Xi -

A pariah in the West since the start of the assault on Ukraine, Putin on Friday spoke by video link with Chinese leader Xi Jinping, calling him a "dear friend" and hailing the two countries' efforts to counter Western "pressure".

Putin also said he was keen to ramp up military cooperation.

"We aim to strengthen cooperation between the armed forces of Russia and China," Putin told Xi, a week after the two countries conducted naval drills in the East China Sea.

Putin also hailed the efforts of Moscow and Beijing to counter "unprecedented Western pressure and provocations" and said he expected Xi to arrive in Moscow for a state visit next spring.

Putin has also relied on the backing of Belarus's long-serving president Alexander Lukashenko, who allowed Russian troops to use his country as a launchpad for the offensive.

In a first, Minsk on Thursday said its forces had downed a Ukrainian air defence missile in the western Brest region that borders Poland and Ukraine, raising fears of a spillover of the conflict.

The authorities in Minsk summoned Ukraine's ambassador to protest the incident.

The Belarusian defence ministry said Friday it was considering the possibility that the incident was a "deliberate provocation" by Ukrainian forces.

The Kremlin said Friday the incident caused "extreme concern" in Minsk and Moscow.

Kyiv has suggested it might have been part of a Russian ploy to try to draw Belarus into the conflict.