Kyiv, Ukraine - Russia's army on Thursday launched a massive attack on Ukraine's energy sector, forcing emergency power outages as temperatures dropped to freezing across the country.

Ukraine's energy grid has been heavily targeted since Russia invaded in February 2022, with Kyiv accusing Moscow of "terror" tactics by trying to plunge Ukrainian cities into darkness and cut off heating to civilians throughout the winter.

The overnight strikes come after two weeks of dramatic escalation that has seen both sides launch new weapons to gain an upper hand ahead of Donald Trump being inaugurated as US president in January.

Ukraine's Energy Minister German Galushchenko said power infrastructure was "under massive enemy attack" after a countrywide air alert was issued for incoming missiles.

Ukraine conflict US "appalled" by Russia's reported use of banned riot gas in Ukraine

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 northeast, 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," Galushchenko said.

National power grid operator Ukrenergo had "urgently introduced emergency power cuts," he added, as temperatures dropped to around 32 degrees Fahrenheit.

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

The nationwide attack was ongoing as of 08:00 AM local time (1 AM ET), according to messages from the air force.

"As soon as the security situation will allow it, the consequences (of the strikes) will be specified," Galushchenko said.

President Volodymyr Zelensky'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."

Joke of the Day Joke of the Night for November 26, 2024: The best Thanksgiving jokes to laugh the day away

Russia earlier this week said it was preparing its own retaliation for Ukrainian strikes on its territory with 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.

The latest missile salvo comes a day after President-elect Trump named staunch loyalist and retired general Keith Kellogg as his Ukraine envoy, charged with ending the Russian invasion.

Trump campaigned on a platform of securing a swift end to the Ukraine war, boasting that he would quickly mediate a ceasefire deal – comments that have triggered concern in Kyiv that the US could push it to cede land.

The outgoing Joe Biden administration has urged Ukraine to drop the minimum age of conscription to 18 to plug severe manpower shortages across the 600-mile front line.

Russian troops have been advancing in the east for months, where they have a manpower and ammunition advantage over Ukraine's stretched forces.