Russia's army on Thursday launched a "massive attack" on Ukraine's energy sector, leaving at least one million people across three western regions without power, local officials said.

Ukraine's Energy Minister German Galushchenko said "attacks on energy facilities are happening all over Ukraine," after a countrywide air alert was issued for incoming missiles.

Explosions were reported in Kyiv, Kharkiv, Rivne, Khmelnytskyi, Lutsk, and many other cities in central and western Ukraine.

The attacks cut power to 523,000 consumers in Lviv region, about 215,000 in Volyn region and over 280,000 in Rivne region, their governors reported on the Telegram messaging app.

The air force reported a string of Russian cruise missiles and attack drones heading for cities across the country, including the capital Kyiv, Kharkiv in the north-east and the Black Sea port city of Odesa.

"Once again, the energy sector is under massive enemy attack. Attacks on energy facilities are taking place across Ukraine," Mr Galushchenko said.

National power grid operator Ukrenergo had "urgently introduced emergency power cuts", he added, as temperatures dropped to around zero degrees Celsius.

Energy provider DTEK said Ukrenergo was introducing emergency power outages in the regions of Kyiv, Odesa, Dnipro and Donetsk.

Strategic timing

President Volodymyr Zelenskyy's chief of staff said the wave of attacks showed Russia was "continuing their tactics of terror".

"They stockpiled missiles for attacks on Ukrainian infrastructure, for warfare against civilians during … winter," Andriy Yermak said in a post on Telegram and pledged that Ukraine would respond.

A senior UN official, Rosemary DiCarlo, this month warned Russian strikes on Ukraine's energy infrastructure may make this winter the "harshest since the start of the war".

Russia earlier this week said it was preparing its own retaliation for Ukrainian strikes on its territory using US-supplied ATACMS missiles.

Ukraine has launched at least three attacks on Russian border regions with the missiles since the White House gave it permission to fire them on Russian territory.

Moscow responded to the first strike by firing a never-before-seen hypersonic ballistic missile at the Ukrainian city of Dnipro.

In an angry address to the nation, Russian President Vladimir Putin warned the nuclear-capable missile could be used against Western countries if they let their arms be used by Ukraine to hit Russia.

Ukraine needs more soldiers, says US

President Joe Biden's administration is urging Ukraine to quickly increase the size of its military by drafting more troops and revamping its mobilisation laws to allow for the conscription of those as young as 18.

A senior Biden administration official, who spoke on the condition of anonymity, said the lowering of the mobilisation age to 18 from the current age of 25 would help get more fighting-age men available to help a badly outnumbered Ukraine.

The official said "the pure math" of Ukraine's situation now is that it needs more troops in the fight.

White House National Security Council spokesman Sean Savett in a statement said the administration will continue sending Ukraine weaponry but believes "manpower is the most vital need" Ukraine has at the moment.

"We're also ready to ramp up our training capacity if they take appropriate steps to fill out their ranks," Mr Savett said.

The Ukrainians have said they need about 160,000 additional troops to keep up with its battlefield needs, but the US said they need more.

Mr Zelenskyy has consistently stated that he has no plans to lower the mobilisation age.

Some Ukrainians have expressed worry that further lowering the minimum conscription age and taking more young adults out of the workforce could backfire by further harming the war-ravaged economy.

Russia takes out more drones

Russia's air defence systems destroyed 25 Ukrainian drones overnight over four regions, the Defence Ministry said on Thursday.

Fourteen of the drones were destroyed over the Krasnodar region, six over the Bryansk region, three over Moscow-annexed Crimea and two over the Rostov region, it said.

Krasnodar's regional governor, Veniamin Kondratyev, wrote on Telegram that two districts in the southern Russian region were subjected to a "massive drone attack" overnight. One civilian was injured, he said.

A local Telegram channel published footage showing an object crashing into a building in the town of Slavyansk-na-Kubani, followed by a loud boom and fireball.