The city of 3 million endured a second night of shelling, with residents hunkering down in basement shelters and the city’s deep underground metro.

Among the strategic sites captured on the first day of the assault was the Chernobyl nuclear power station north of Kyiv, where staff still oversee the plant, though no reactors are in operation 36 years after the world’s worst nuclear accident.

The United Kingdom is ready to guarantee loans of up to $500 million to support Ukraine and mitigate the economic consequences of Russian aggression. Italy is ready to allocate 110 million euros.

Western countries denounced the Russian incursion, launched as the U.N. Security Council was debating the prospect of intervention, and pledged to introduce tough punitive measures on the Kremlin.

It was not immediately clear whether Moscow's forces had formally moved into the parts of Ukraine’s Donetsk and Luhansk region controlled by separatists – most analysts and Ukrainian officials have said that some Russian forces have long been informally established inside them.