Russian troops stormed toward Ukraine’s capital early Saturday as explosions reverberated through the city but President Volodymyr Zelenskyy urged the country to “stand firm” against the siege that could determine its future. He refused American help to evacuate, saying: “The fight is here.”

Hundreds of casualties were reported in the fighting, which included shelling that sliced through a Kyiv apartment building and pummelling bridges and schools. There also were growing signs that Russia may be seeking to overthrow Ukraine’s government, which US officials have described as Russian President Vladimir Putin’s ultimate objective.

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The assault represented Putin’s boldest effort yet to redraw the world map and revive Moscow’s Cold War-era influence. It triggered new international efforts to end the invasion, including direct sanctions on Putin.

As his country confronted explosions and gunfire, and as the fate of Kyiv hung in the balance, Ukraine President Volodymyr Zelensky appealed for a cease-fire and warned in a bleak statement that multiple cities were under attack.

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“Tonight we have to stand firm,” he said. “The fate of Ukraine is being decided right now.”

Zelensky was urged to evacuate Kyiv at the behest of the U.S. government but turned down the offer, according to a senior American intelligence official with direct knowledge of the conversation. The official quoted the president as saying that “the fight is here” and that he needed anti-tank ammunition but “not a ride.”

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For their part, the US defence officials believe the Russian offensive has encountered considerable resistance and is proceeding slower than Moscow had envisioned, though that could change quickly.

The Kremlin accepted Kyiv’s offer to hold talks, but it appeared to be an effort to squeeze concessions out of the embattled Zelensky instead of a gesture toward a diplomatic solution.

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The Russian military continued its advance, laying claim Friday to the southern Ukraine city of Melitopol. Still, it was unclear in the fog of war how much of Ukraine is still under Ukrainian control and how much or little Russian forces have seized.