Washington DC - President Joe Biden has cleared Kyiv to use long-range American missiles against military targets inside Russia, a US official told AFP on Sunday, hours after Russia targeted Ukraine's power grid in a deadly barrage.

The official, speaking on condition of anonymity, was confirming reports from The New York Times and The Washington Post that the major policy shift – long demanded by Ukraine – was in response to North Korea deploying troops to help Moscow's war effort.

Ukrainian President Volodymyr Zelensky has long pushed for authorization from Washington to use the powerful Army Tactical Missile System, known by its initials ATACMS, to hit targets inside Russia.

Poland was among the first to welcome the development.

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"With the entry into the war of North Korea troops and (Sunday's) massive attack of Russian missiles, President Biden responded in a language that (Russian President) V.Putin understands," Foreign Minister Radoslaw Sikorski posted on X.

"The victim of aggression has the right to defend himself," he added.

Zelensky's response, in his evening address Sunday, was more muted, referring to the military's "long range capability" as one of the main points of Ukraine's victory plan.

"Today, there are many media reports that we have received permission to take appropriate actions," he said.

"But strikes are not made with words. Such things are not announced. The missiles will speak for themselves. Definitely."

News of Biden's decision came hours after Ukraine announced nationwide emergency power restrictions from Monday after Russia's massive attack, which killed 11 civilians and further damaged the country's already fragile energy grid.

Another 10 people were killed, including two children, in another strike Sunday evening in the northeast town of Sumy.

State power company Ukrenergo announced the power cuts on Sunday, with Ukraine's much-feared winter approaching.

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Russia's latest barrage brought swift international condemnation.

UN Secretary-General Antonio Guterres denounced the attack, which his spokesperson Stephane Dujarric said in a statement had targeted "energy and critical civilian infrastructure."

Zelensky said Moscow launched 120 missiles and almost 100 drones, targeting Kyiv as well as southern, central, and far-western corners of the country.

The attack, which officials said was one of Russia's largest, came as the war neared its 1,000th day, which will be marked at the United Nations on Monday, attended by Ukraine's Foreign Minister Andriy Sybiga.

Civilians were killed in the Mykolaiv, Lviv, Kherson, Dnipropetrovsk, and Odesa regions.

Many fear a third winter of war will be the toughest yet. Previous Russian attacks have already destroyed half of Ukraine's energy production capacity, Zelensky has warned.

Moscow said it had hit all its targets, saying it had aimed for an "essential energy infrastructure supporting the Ukrainian military-industrial complex."

But civilian deaths were reported across the country from the strikes overnight Saturday to Sunday.

Russia said Ukrainian drones attacks had killed a man in its border Belgorod region and a woman – named as local journalist Yulia Kuznetsova – in the border Kursk region.

Kursk leader Alexei Smirnov said she had been reporting on the "situation in the region," where a Ukrainian incursion has displaced thousands of people.

The West and Ukraine say thousands of North Korea soldiers are in Russia, with some in the Kursk region, to reinforce Moscow's forces.

Meanwhile, the US has provided more than $64.1 billion in military aid to Ukraine since 2022.

The imminent return of Donald Trump to the White House has called into question future US military support for Kyiv.