KYIV: More than a million Ukrainians were left without power in freezing cold temperatures on Thursday after a massive nationwide Russian missile and drone attack.

Ukraine is bracing for what could be its toughest winter of the almost three-year war as Moscow steps up its aerial bombardment of the war-torn country and its troops advance on the frontlines in the east.

“There are emergency blackouts all over the country due to the enemy’s attack on our energy sector. There is no end in sight,” said the CEO of the Yasno energy supplier Sergey Kovalenko.

President Volodymyr Zelensky’s chief of staff said Russia was “continuing their tactics of terror,” seeking to plunge Ukrainian civilians into darkness and cut of heating in the coldest months of the year.

“They stockpiled missiles for attacks on Ukrainian infrastructure, for warfare against civilians during... winter,” Andriy Yermak said in a post on Telegram.

The combined missile and drone attack, launched in waves throughout the early hours of Thursday, knocked out electricity for more than a million subscribers in Ukraine’s west, hundreds of kilometers from the front lines.

“As of now, 523,000 subscribers in Lviv region are without electricity,” regional head Maksym Kozytskyi said on social media.

The western region, which borders EU and NATO member Poland, has been spared the worst of the fighting of Russia’s 33-month invasion but has been targeted in Russian drone and missile attacks sporadically.

Regional officials said at least another 280,000 were cut off in the western Rivne region and another 215,000 in the northwestern Volyn region, which also borders Poland.

The full extent of the damage was still being assessed on Thursday morning, with Russian drones also having targeted the capital Kviv, the northeastern city of Kharkiv and port city of Odesa on the Black Sea and other regions reporting power outages.

“Power engineers are working to ensure backup power supply schemes where possible. They have already started restoration work where the security situation allows,” the energy ministry said.

It said it was the 11th massive Russian attack on Ukraine’s civilian energy infrastructure this year.

In an early morning warning posted on social media as the strikes were unfolding, Ukraine’s Energy Minister German Galushchenko said facilities were “under massive enemy attack.”

The strikes, which came as temperatures hit 0 degrees Celsius in many Ukrainian cities, are the latest in two weeks of dramatic escalation in the near three-year war.

A senior UN official, Rosemary DiCarlo, this month warned Russian attacks on Ukraine’s energy infrastructure may make this winter the “harshest since the start of the war.”

Both sides have fired new weapons in an attempt to gain an upper hand ahead of Donald Trump being inaugurated as US president in January.

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

Kyiv 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 and Russian President Vladimir Putin warned the nuclear-capable missile could be used against Western countries next.

Trump on Wednesday named staunch loyalist and retired general Keith Kellogg as his Ukraine envoy, charged with ending the Russian invasion.

The incoming president has criticized US aid to Ukraine and boasted he could secure a ceasefire in hours — comments that have triggered concern in Kyiv that the US could push it to cede land.

Kellog, an 80-year-old national security veteran, co-authored a paper this year calling for Washington to leverage military aid as a means of pushing for peace talks.

Concerned at a string of Russian advances on the frontline, the outgoing Joe Biden administration has also urged Ukraine drop the minimum age of conscription from 25 to 18 to plug severe manpower shortages.

Russia’s defense ministry also said Thursday it had downed 25 Ukrainian drones fired overnight, including 14 over the southern Krasnodar territory — just to the east of the annexed Crimean peninsula.