Amid growing accusations of war crimes, Ukrainian forces and residents of Mariupol have continued what the government called their "heroic" resistance to a brutal Russian attack as the Ukrainian president restated his call for peace talks even as he took a defiant stand against the Kremlin's surrender ultimatums.
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As Mariupol's Ukrainian defenders battled to stave off the deadly onslaught on March 21, Russian forces intensified and broadened their attacks elsewhere, including on the capital, Kyiv, where an air strike on a shopping mall and nearby apartment building killed at least eight people.
Ukrainian President President Volodymyr Zelenskiy remained defiant as Kyiv rejected a Russian ultimatum to surrender Mariupol, saying Ukraine could never give up the strategic port or other cities, including Kharkiv and the capital.
In comments to local media on March 21, Zelenskiy accused Moscow of trying to "destroy" his country. "Ukraine cannot fulfill Russian ultimatums," he said. "We should be destroyed first, then their ultimatum would be fulfilled."
He said the Russians wanted Ukraine to "hand over" the cities of Kyiv, Kharkiv, and Mariupol but that neither the Ukrainian people "nor me, as president, can do this."
In an interview with news site Suspilne on March 21, Zelenskiy restated his insistence on the need to meet with Russian President Vladimir Putin "in any format" to end the fighting.
"I believe that without this meeting, it is impossible to fully understand what they are ready for in order to stop the war," said Zelenskiy, who added that any compromises made in talks with Russians would be put before the Ukrainian people in a referendum.
But Kremlin spokesman Dmitry Peskov said on March 21 that "significant progress" in the peace talks between negotiators is needed before a meeting between Putin and Zelenskiy would be a possibility.
Mariupol: Apocalyptic Images From A City Under Siege
Russia has for the past two weeks attempted to encircle Mariupol, an important port on the Sea of Azov. It is seeking to take control of the city, allowing it to link Crimea -- which it seized in 2014 -- with territory controlled by Kremlin-backed separatists in eastern Ukraine.
At least 2,300 people have died in Mariupol, some buried in mass graves, authorities have said.
On March 20, an attack destroyed an art school sheltering some 400 people in the city. There was no immediate report on casualties, but authorities fear many people could still be under the rubble.
WATCH: Russian troops occupying the southern Ukrainian city of Kherson fired live rounds and stun grenades at peaceful protesters. Amateur video showed at least one person being wounded.
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Russian Troops Open Fire On Ukrainian Protesters In Kherson
That attack came after Russian air strikes on March 16 flattened a theater in Mariupol where civilians were also sheltering. City authorities said 130 people were rescued but many more could remain under the debris.
In addition, Russian forces have been accused of bombing a maternity hospital in the city, where an estimated 90 percent of the buildings have been damaged or destroyed.
The U.S. military on March 21 accused Russian forces of committing war crimes in their bloody invasion of Ukraine.
"We certainly see clear evidence that Russian forces are committing war crimes and we are helping with the collecting of evidence of that," Pentagon spokesman John Kirby told a news briefing.
Earlier, Josep Borrell, the European Union's top diplomat, said that "what's happening now in Mariupol is a massive war crime, destroying everything, bombarding and killing everybody."
Ukrainian Defense Minister Oleksiy Reznikov hailed Mariupol's "heroic defenders" after authorities rejected an ultimatum by Russia to give up the besieged city as of 5 a.m., saying there was “no question of any surrender.”
Reznikov said their resistance was slowing the progress of Russia's military and disrupting attempts to subjugate other Ukrainian cities.
"By virtue of their dedication and superhuman courage, tens of thousands of lives throughout Ukraine were saved. Today, Mariupol is saving Kyiv, Dnipro, and Odesa," he said.
Residents of Mariupol, which had a population of 400,000 before the war broke out, have for the past two weeks been trapped without basic supplies, such as water, food, and fuel.
In Kyiv, air strikes hit the Retroville shopping mall in the northwest outskirts of the capital late on March 20, killing at least eight people. The mall, surrounded by several high-rise apartment buildings in the Podil neighborhood of Kyiv, was still smoldering on the morning of March 21.
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Taking Calls On Ukraine's Help Line For Russian Military Moms
RFE/RL correspondents saw devastating scenes in the area, with workers attempting rescue efforts as ambulances, police, and firefighters converged on the area.
One man, who said he lives about a kilometer away, told RFE/RL: “I have never felt the earth shake like that. It was a powerful explosion."
“They are killing my city. They are killing the place where I live,” he added.
Hours after the attack, Vitali Klitschko, the Ukrainian capital's mayor, announced a new 35-hour curfew to come into force at 8 p.m. on March 21.
Russia invaded Ukraine on February 24, but Ukrainian forces have mounted stiff resistance and the West has imposed sweeping sanctions on Moscow in an effort to force it to withdraw its forces.
Poland and the Baltics are pushing for tougher sanctions, including an EU ban on Russian oil and gas imports. However, Germany, which is heavily dependent on Russian gas, and some other EU member states are resisting.
WATCH: People in Kyiv voiced shock after a massive Russian air strike destroyed a shopping mall and also hit residential buildings. At least eight people were reported to have been killed.
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'They're Killing My City': Shock In Kyiv After Strike On Mall
Peskov said Europe would be hit hard in the event of an embargo on Russian oil, striking the continent's energy balance.
The Russian military claimed that it had for the first time in combat used its state-of-the-art hypersonic missile to hit particularly important targets in Ukraine, a move widely condemned in the West.
Russian Defense Ministry spokesman Major General Igor Konashenkov said on March 21 that the Kinzhal hypersonic missile “has proven its efficiency in destroying heavily fortified special facilities.”
Russia has denied targeting civilians, despite incontrovertible evidence of deadly attacks on nonmilitary sites.
Observers have speculated that Russian military momentum has been stopped by Ukrainian forces in many parts of the country and that the sides could be heading for a long, protracted stalemate in the war.
Filippo Grandi, head of the UN's refugee agency said on March 20 that at least 10 million of Ukraine's population of 44 million people have fled their homes.
About 3.4 million have fled across Ukraine's borders to neighboring countries, with the bulk of them arriving in NATO and European Union member Poland.