Ukrainian forces dug in and Russia's military lined up more firepower Sunday ahead of an expected showdown in eastern Ukraine that could become a decisive period in a war that has flattened cities, killed untold thousands and isolated Moscow economically and politically.
Experts say a full-scale offensive in the east could start within days, though questions remained about the ability of Russia's depleted and demoralized forces to conquer much ground after Ukraine's inspired defenders repelled their push to capture the capital, Kyiv.
Britain's Defense Ministry reported Sunday that Russia's armed forces were trying to compensate for mounting casualties by boosting troop numbers with personnel who had been discharged from service since 2012. Ukraine has the bulk of its military forces in the east: estimates vary, but they are believed to number in the tens of thousands.
Russia-backed separatists have fought Ukrainian forces in eastern Ukraine since 2014 and control parts of the Donbas, a mostly Russian-speaking, industrial region. Since Russia invaded Ukraine on Feb. 24, its troops have bombarded government-held territory. The anticipated offensive in the east and south could end up excising a vast swath of land from Ukraine.
On Sunday, Russian forces shelled Kharkiv, Ukraine's second-largest city, in the northeast and sent reinforcements toward Izyum to the southeast in attempts 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.
Russia's sea-launched cruise missiles also 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.
Ukrainian President Volodymyr Zelenskyy appealed for stronger military and political support from the West, including NATO members that have funneled weapons and military equipment to Ukraine since Russia invaded but denied some requests for fear of getting drawn into the war.
In a late night video message, Zelenskyy argued that more than Ukraine's future was at stake: Russia's aggression "was not intended to be limited to Ukraine alone" and the "entire European project is a target," he said.
"That is why it is not just the moral duty of all democracies, all the forces of Europe, to support Ukraine's desire for peace," Zelenskyy said. "This is, in fact, a strategy of defense for every civilized state."
Zelenskyy thanked the president of the European Union's executive commission and Canada's prime minister for a global fundraising event Saturday that brought in more than $11 billion to help Ukrainians who have fled the war.
The U.N. refugee agency reported Sunday that more than 4.5 million people have left the country since the invasion started Europe's worst ground conflict since World World II. As of Friday night, the U.N.'s human rights commissioner had confirmed 1,766 civilian deaths from more than six weeks of fighting - - 630 of them in the Donbas - while acknowledging the toll was likely a vast undercount.
After British Prime Minister Boris Johnson went to Kyiv on a Saturday trip that the U.K. government did not announce in advance, Zelenskyy said they had decided "what help the United Kingdom will provide to the post-war reconstruction of Ukraine" and that it includes a "patronage" to rebuild the Kyiv region.
Ukrainian authorities have accused Russian forces of committing war crimes against thousands of civilians during the invasion. The alleged crimes took place during airstrikes on hospitals, a missile attack that killed 52 people at a train station in eastern Ukraine on Friday and as Russian soldiers withdrew from the outskirts of Kyiv.
Zelenskyy said that when he and German Chancellor Olaf Scholz spoke by phone Sunday, "we emphasized that all perpetrators of war crimes must be identified and punished."
Ukraine has blamed Russia for alleged atrocities against civilians in Bucha and other towns outside the capital where hundreds of bodies, many with their hands bound and signs of torture, were found after the Russian troops retreated. Russia has denied engaging in war crimes and falsely claimed that the scenes in Bucha were staged.
After the Russian forces pulled out from the north this week to regroup for the push in the east, firefighters combed through the rubble of buildings to search for victims or survivors. Maria Vaselenko, 77, a resident of Borodyanka, said her daughter and son-in-law were killed, leaving her grandchildren orphaned.
"The Russians were shooting. And some people wanted to come and help, but they were shooting them. They were putting explosives under dead people," Vaselenko said. "That's why my children have been under the rubble for 36 days. It was not allowed" to remove bodies.
In Mariupol, Russia was deploying Chechen fighters, reputed to be particularly fierce. Capturing the city on the sea of Azov would give Russia a land bridge to the Crimean Peninsula, which Russia seized from Ukriane eight years ago.
Residents have lacked food, water and electricity since Russian forces surrounded the city, making evacuations hard and supplying emergency relief even harder.
Zelenskyy has said he expects more evidence of atrocities to be found once Mariupol no longer is blockaded; Ukrainian authorities think an airstrike on a theater where civilians were sheltering killed hundreds.
"I am in shock. I don't understand what is happening. I have a hole in my garage billowing smoke," Mariupol resident Sergey Petrov told The Associated Press, describing a brush with death. "A shell flew in and broke up into two parts, but it did not explode. … My mother told me that I was born again on that day."
Ukrainian Deputy Prime Minister Iryna Vereshchuk said more civilians were expected to leave Mariupol in their personal vehicles Sunday, while more evacuations were planned for a number of towns in the south and east.
The Institute for the Study of War, an American think tank, predicted Russian forces would focus their assault on the northern edge of a sickle-shaped arc of eastern Ukraine where the pro-Russia separatists and Russian forces have seized territory.
Russian forces will "renew offensive operations in the coming days" from Izyum, a town southeast of Kharkiv, to try to reach Slovyansk, even further southeast, the institute's analysts said. But in their view, "The outcome of forthcoming Russian operations in eastern Ukraine remains very much in question."
Ukrainian officials have pleaded with Western powers almost daily to send more arms and further punish Moscow with sanctions, including the exclusion of Russian banks from the global financial system and a total EU embargo on Russian gas and oil.
In an interview with The Associated Press inside his heavily guarded presidential office complex on Saturday, Zelenskyy said he was committed to negotiating a diplomatic end to the war even though Russia has "tortured" Ukraine.
He also acknowledged that peace likely will not come quickly. Talks so far have not included Putin or other top Russian officials.
"We have to fight, but fight for life. You can't fight for dust when there is nothing and no people. That's why it is important to stop this war," the president said.
In the interview with AP, Zelenskyy noted the increased support but expressed frustration when asked if weapons and equipment Ukraine has received from the West is sufficient to shift the war's outcome.
"Not yet," he said, switching to English for emphasis. "Of course it's not enough."
Additional reporting by the Associated Press.