Russian forces appeared to make progress from the northeast in their slow fight toward Ukraine’s capital, while tanks and artillery pounded places already under siege with shelling so heavy that residents of one city were unable to bury the growing number of dead.

In past offensives in Syria and Chechnya, Russia’s strategy has been to crush armed resistance with sustained airstrikes and shelling that levels population centers. That kind of assault has cut off the southern port city of Mariupol, and a similar fate could await Kyiv and other parts of Ukraine if the war continues.

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In Mariupol, unceasing barrages into the city have thwarted repeated attempts to bring in food and water and evacuate trapped civilians. On Friday, an Associated Press photographer captured the moment when a tank appeared to fire directly on an apartment building, enveloping one side in a billowing orange fireball.

A deadly strike on a maternity hospital there this week sparked international outrage and war-crime allegations.

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Mariupol’s death toll has passed 1,500 in 12 days of attack, the mayor’s office said. Shelling forced crews to stop digging trenches for mass graves, so the “dead aren’t even being buried,” the mayor said.

Invading Russian forces have struggled far more than expected against determined Ukrainian fighters. But Russia’s stronger military threatens to grind down Ukrainian forces, despite an ongoing flow of weapons and other assistance from the West for Ukraine’s westward-looking, democratically elected government.

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The conflict has already sent 2.5 million people fleeing the country.

On the ground, the Kremlin’s forces appeared to be trying to regroup and regain momentum after encountering heavy losses and tough resistance over the past two weeks. Britain’s Ministry of Defence said Russia is trying to reset and “re-posture” its troops, gearing up for operations against Kyiv.