Kyiv (AFP) - Ukraine on Wednesday appealed for Western military help, ahead of an emergency NATO summit, and denounced Russian "war crimes" in besieged places including the port of Mariupol where it says mass starvation is possible.
Tens of thousands of residents have already fled the southern city, bringing harrowing testimony of a "freezing hellscape riddled with dead bodies and destroyed buildings", according to Human Rights Watch.
But Ukrainian President Volodymyr Zelensky said that almost 100,000 people remained trapped by relentless Russian bombardment in Mariupol without water, food and power.
The mayor of Kyiv, former world heavyweight boxing champion Vitali Klitschko, said Ukrainian forces were pushing the invaders back in several areas around the capital.
"We are ready to fight for each building, each street, every part of our city," he told reporters."We would rather die than kneel in front of the Russians or surrender to the invaders."
As President Joe Biden travelled to the summits of NATO, the G7 and European Union in Brussels, Andriy Yermak, a top advisor to Zelensky, said Ukraine was holding out "with superhuman courage".
"But we cannot win a war without offensive weapons, without medium-range missiles that can be a means of deterrence," Yermak said.
'Ruins of Verdun'
NATO chief Jens Stoltenberg said the leaders at Thursday's summit would agree to "major increases of forces" including four new battle groups in Bulgaria, Hungary, Romania and Slovakia.
The allies will also offer "additional support" to Kyiv against nuclear and chemical threats, he said, after Biden warned anew that Russia could be prepared to unleash Syria-style horror in Ukraine.
But NATO members, while maintaining a steady supply of anti-tank and anti-aircraft missiles, have balked at Zelensky's demands to impose a no-fly zone over Ukraine, fearing all-out war with nuclear-armed Russia.
Zelensky kept up the pressure on foreign allies, using speeches to French and Japanese lawmakers to invoke their own national traumas of the past.
He told the French National Assembly that images of devastated cities such as Mariupol "recall the ruins of Verdun as in the photos of World War I that everyone has seen".
"The Russian army makes no distinction between targets.They destroy residential areas, hospitals, schools, universities.
"They do not take into account the concepts of war crimes."
Nearly a month on in to the invasion, peace talks have agreed on daily humanitarian corridors for refugees, and Ukraine says it is willing to countenance some Russian demands subject to a national referendum.
But it has refused to bow to Russian pressure to disarm and renounce all Western alliances, and Zelensky was also due Thursday to address the NATO meeting.
Ukraine's lead negotiator Mykhaylo Podolyak said the peace talks were encountering "significant difficulties", after Moscow accused the United States of undermining the process.
Russia meanwhile refuses to rule out using nuclear weapons if it faces an "existential threat", Kremlin spokesman Dmitry Peskov told CNN.
Pentagon spokesman John Kirby slammed Moscow's "dangerous" rhetoric.
Charred landscape
For Ukrainians besieged in Mariupol and other cities, Russian talk of peace rings hollow as they come under indiscriminate shelling that Western countries agree amounts to a war crime.
Satellite images of Mariupol released by private company Maxar showed a charred landscape, with several buildings ablaze and smoke billowing from the city.
Ukrainian forces also reported "heavy" ground fighting, with Russian "infantry storming the city" after they rejected a Monday ultimatum to surrender.
"Even if Mariupol falls, Ukraine cannot be conquered city by city, street by street, house by house," United Nations chief Antonio Guterres said.
"This war is unwinnable. Sooner or later, it will have to move from the battlefield to the peace table.That is inevitable."
Mariupol is a pivotal target in President Vladimir Putin's war -- providing a land bridge between Russian forces in Crimea to the southwest and Russian-controlled territory to the north and east.
Putin threatens 'Russia's future'
"Putin's offensive is stuck despite all the destruction that it is bringing day after day," German Chancellor Olaf Scholz said in a speech to the Bundestag, warning of further Western sanctions against Russia.
Putin "must hear the truth" that not only is the war destroying Ukraine, "but also Russia's future", he said.
After Brussels, Biden will head on to Poland, which has received the bulk of more than 3.6 million Ukrainians fleeing the war.
The president will consult with allies on new sanctions and on potentially throwing Russia out of the G20, US officials said.
"We believe that it cannot be business as usual for Russia in international institutions and in the international community," White House National Security Advisor Jake Sullivan told reporters.
China, a leading member of the G20, pushed back against expelling Russia from the group of major economies, and Moscow said Putin still intended to join its November summit in Indonesia.
Stoltenberg said NATO feared that China could go further in its backing of Russia by providing material support, although US officials said there was no sign of that happening since Biden held a crunch phone call with President Xi Jinping last week.
The NATO chief demanded that China stop giving Russia diplomatic cover, and stop "spreading blatant lies and misinformation" on its behalf.
On the ground, Russia's defence ministry has reported some advances in the southeast of Ukraine and boasted of strikes using next-generation weaponry against "military infrastructure" across the country.
But Ukraine and its allies have claimed Russian forces are severely depleted, poorly supplied and still unable to carry out complex operations.
'Morale is high'
In the southern city of Mykolaiv, one bulwark of the Ukrainian fightback, residents said they were determined to stay despite incessant bombardment.
At the burial of soldier Igor Dundukov, 46, his brother Sergei wept as he kissed his sibling's swollen, blood-stained face.
"We supported his commitment to defending our homeland," Sergei told AFP."This is our land.We live here.Where would we run to?We grew up here."
In the capital Kyiv, lawyer Maxim Kostetskyi, 29, said morale remained high.
"We don't know if the Russians will continue with their efforts to encircle the city, but we are much more confident, the morale is high and inspiring," he told AFP.
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