A young man pushes a wheelbarrow in front of a destroyed apartment building in the town of Borodyanka, Ukraine, on Sunday, April 10, 2022. Several apartment buildings were destroyed during fighting between the Russian troops and the Ukrainian forces and the town is without electricity, water and heating. (AP Photo/Petros Giannakouris)

KYIV, Ukraine — As Ukrainian forces dug in on Sunday, Russia lined up more firepower and tapped a decorated general to take centralized control of the war ahead of a potentially decisive showdown in eastern Ukraine that could start within days.

Ukrainian President Volodymyr Zelenskyy warned Sunday in his nightly address to the nation that the coming week would be as crucial as any in the war, saying “Russian troops will move to even larger operations in the east of our state.”

He also accused Russia of trying to evade responsibility for war crimes in Ukraine.

“When people lack the courage to admit their mistakes, apologize, adapt to reality and learn, they turn into monsters. And when the world ignores it, the monsters decide that it is the world that has to adapt to them,” Zelenskyy said.

“The day will come when they will have to admit everything. Accept the truth,” he added.

Experts have said that the next phase of the battle may begin with a full-scale offensive. The outcome could determine the course of the conflict, which has flattened cities, killed untold thousands and isolated Moscow economically and politically.

Questions remain about the ability of Russia’s depleted and demoralized forces to conquer much ground after their advance on the capital, Kyiv, was repelled by determined Ukrainian defenders. Britain’s Defense Ministry reported Sunday that the Russian forces were trying to compensate for mounting casualties by recalling veterans discharged in the past decade.

In Washington, a senior U.S. official said that Russia has appointed Gen. Alexander Dvornikov, one of its most seasoned military chiefs, to oversee the invasion. The official was not authorized to be identified and spoke on condition of anonymity.

Until now, Russia has had no central war commander on the ground.

The new battlefield leadership comes as the Russian military prepares for what is expected to be a large, focused push to expand control in Ukraine’s east. Russia-backed separatists have fought Ukrainian forces in the eastern Donbas region since 2014 and declared some territory there as independent.

Dvornikov, 60, gained prominence as head of the Russian forces deployed to Syria in 2015 to shore up President Bashar Assad’s government during the country’s devastating civil war. U.S. officials say he has a record of brutality against civilians in Syria and other war theaters.

Russian authorities do not generally confirm such appointments and have said nothing about a new role for Dvornikov, who received the Hero of Russia medal, one of the country’s highest awards, from President Vladimir Putin in 2016.

U.S. national security adviser Jake Sullivan, speaking Sunday on CNN’s “State of the Union,” played down the significance of the appointment.

“What we have learned in the first several weeks of this war is that Ukraine will never be subjected to Russia,” Sullivan said. “It doesn’t matter which general President Putin tries to appoint.”

Western military analysts say Russia’s assault has increasingly focused on a sickle-shaped arc of eastern Ukraine — from Kharkiv, Ukraine’s second-largest city, in the north to Kherson in the south.

The narrower effort could help Russia’s problem, earlier in the war, of spreading its offensive too widely over too great a geographic area.

“Just looking at it on a map, you can see that they will be able to bring to bear a lot more power in a lot more concentrated fashion,” by focusing mainly on eastern Ukraine, Pentagon spokesman John Kirby said Friday.

Newly released Maxar Technologies satellite imagery showed an 8-mile (13-kilometer) convoy of military vehicles headed south through Ukraine to Donbas, recalling images of a convoy that got stalled on roads to Kyiv for weeks before Russia gave up on trying to take the capital.

On Sunday, Russian forces shelled government-controlled Kharkiv and sent reinforcements toward Izyum to the southeast in a bid to break Ukraine’s defenses, the Ukrainian military command said. The Russians also kept up their siege of Mariupol, a key southern port that has been under attack and surrounded for nearly 1 ½ months.

A Russian Defense Ministry spokesman, Maj. Gen. Igor Konashenkov, said Russia’s military used air-launched missiles to hit Ukraine’s S-300 air-defense missile systems in the southern Mykolaiv region and at an air base in Chuhuiv, a city not far from Kharkiv.

Sea-launched Russian cruise missiles destroyed the headquarters of a Ukrainian military unit stationed farther west in the Dnipro region, Konashenkov said. Neither the Ukrainian nor the Russian military claims could be independently verified.

The airport in Dnipro, Ukraine’s fourth-largest city, was also hit by missiles twice on Sunday, according to the regional governor.

On Sunday night, Zelenskyy again called on Western countries to provide more assistance to Ukraine