Day 2 of Putin’s attack on Ukraine brought airstrikes and ground battles to cities across the country while threatening mass casualties, economic chaos and Europe’s gravest security crisis in decades.

Zelenskyy said Russia had been targeting civilians and residential areas, something that is denied by Moscow, which as recently as Tuesday was saying it would not invade.

Ukraine’s leader said Thursday that he was Russia’s “No. 1 target” — backing up Western intelligence that Russia intends to decapitate his Western-leaning government and possibly replace it with a regime closer to Moscow.

The United Nations said it had confirmed that at least 25 people had been killed across Ukraine but acknowledged that these were likely underestimates, estimating up to 4 million could flee if the fighting escalates.

Kuleba, Ukraine’s foreign minister, accused Russia of attacking a Ukrainian kindergarten and orphanage in what he described as “war crimes.” NBC News was unable to verify the allegations.

Karim Khan, a prosecutor at the International Criminal Court, said he was watching the conflict with “increasing concern” and said his office may investigate possible war crimes in the country.

Amnesty International condemned Putin’s offensive and called on Russian troops to “immediately stop carrying out indiscriminate attacks in violation of the laws of war.”

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Zelenskyy said in a statement that at least 137 people had been killed and 316 had been injured during the first day of the invasion. Meanwhile, the Ukrainian government said Saturday that Russia had lost as many as 3,000 personnel, more than a dozen aircraft and 102 tanks.

NBC News has not confirmed the numbers of any injuries or deaths on either side.

International condemnation of Russia grew louder on Friday amid reports of civilian casualties.

NATO leaders called the attack “brutal and wholly unprovoked and unjustified,” in a news release which said Russia bore “full responsibility for this conflict” and would “pay a severe price, both economically and politically, for years to come.”

They added that they had drawn up defense plans and “deployed defensive land and air forces in the eastern part of the Alliance, and maritime assets across the NATO area.”

Pope Francis went to the Russian Embassy in Rome to relay his concern over the invasion to Moscow’s ambassador, Vatican spokesman Matteo Bruni said, an unprecedented departure from diplomatic protocol.

In Kazakhstan, a former Soviet republic and one of Russia’s closest allies, the government said it was denying Moscow’s request to send Kazakh troops to join Russian forces in Ukraine. It also said it would not recognize the Luhansk People’s Republic (LNR) and the Donetsk People’s Republic (DNR) — the two Moscow-backed breakaway regions in Ukraine that Putin formally recognized as independent earlier in the week.

Against this backdrop of growing global pressure, there were mixed messages from the Kremlin.

Dmitry Peskov, a Putin spokesman, said Moscow was ready to discuss Ukraine’s earlier offer of talks about realigning the country so it had a “neutral status” between Russia and the West.

Putin held a phone call with Chinese President Xi Jinping on Friday, with the Kremlin claiming in a readout that the Russian leader was ready to send a delegation to Minsk for negotiations with Ukrainian representatives.

But hours later, Putin used a televised meeting of his Security Council to call on the Ukrainian military to “take power into your own hands” because it would be easier for Russia to negotiate with the army, than with Zelenskyy.

Lavrov had earlier suggested that Moscow would only enter talks once Ukraine had laid down its weapons.