Il Nuovo Postiglione - 'Hellscape' in Mariupol as UN chief pleads for Ukraine

The strategic port on the Azov sea has suffered relentless shelling but Ukrainian officials say it has not yet been captured as Russia's invasion, which began almost a month ago, splutters to a halt.

More than 200,000 people are trapped in the city described by those who managed to escape as a "freezing hellscape riddled with dead bodies and destroyed buildings", Human Rights Watch said.

"We know that there will not be enough space for everyone (to evacuate on Tuesday, but) we will try to carry out the evacuation until we have gotten all the inhabitants," vowed Deputy Prime Minister Iryna Vereshchuk in a video address.

Two "super powerful bombs" slammed into the city as rescue efforts were ongoing, according to Mariupol authorities.

As US President Joe Biden readied for a trip to Europe this week to tackle a crisis that risks spiralling into global conflict, United Nations chief Antonio Guterres called for Russia to end its "absurd war."

"Even if Mariupol falls, Ukraine cannot be conquered city by city, street by street, house by house," he said.

"This war is unwinnable. Sooner or later, it will have to move from the battlefield to the peace table. That is inevitable."

- 'We live here' -

With the Russian offensive stalled, Biden has warned that President Vladimir Putin was considering using chemical and biological weapons.

Officials in Washington said Tuesday that Ukraine forces have even reversed battlefield momentum and reclaimed some ground in recent days, particularly in the south of the country.

Russian troops were running out of fuel and food, and the military was beset by communication problems, even reduced to using mobile phones, Pentagon spokesman John Kirby said.

The assessment was corroborated by Ukraine's army command which said Russian troops now had ammunition, food and fuel to last just three days.

In the southern city of Mykolaiv, one bulwark of the fierce resistance, residents said they were determined to stay and defend it 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."

The Ukrainian army said on Facebook that 300 Russian soldiers have defected in the north-eastern Sumy region. And even in areas Russia has captured, resistance has persisted.

In the occupied southern city of Kherson, Ukraine's leaders on Tuesday accused Russian troops of firing on unarmed protesters.

Videos posted on social media and the messaging app Telegram showed citizens gathering in Kherson's "Freedom Square" protesting against Russia's recent seizure of the city.

Russian soldiers could be seen firing into the air.

Ukraine's foreign ministry said in a statement that the humanitarian situation was rapidly deteriorating in Kherson, accusing Moscow of refusing to allow for an aid corridor to evacuate civilians and channel in food.

Biden is due to travel to Brussels on Thursday for a series of summits gathering NATO, EU and G7 leaders, before heading to Poland, which has received the bulk of more than 3.5 million Ukrainians fleeing war in their country.

The two sides are holding negotiations remotely after talks between delegations meeting on the border of Belarus and Ukraine made little progress.

Ukrainian leader Volodymyr Zelensky said all issues would be on the table if Putin agreed to direct talks, including the contested eastern region of Donbas and the annexed Crimea peninsula.

But Zelensky warned his country would be "destroyed" rather than surrender.

- More sanctions -

Since Russia launched its invasion on February 24, at least 117 children have been killed in the war, Ukraine's federal prosecutor said.

Some 548 schools have been damaged, including 72 completely destroyed.

Russia has pushed on with its assaults, in the face of unprecedented Western sanctions that has led international companies to pull out of the country and left its key banks shut out of the SWIFT system.

More sanctions against Russia and tightening of existing measures will be announced Thursday when Biden meets European allies in Brussels.

European Union foreign policy chief Josep Borrell had described as a "massive war crime" the siege of Mariupol, which has killed more than 2,000 people.

Russia had given Mariupol until Monday morning to surrender, but Kyiv rejected the ultimatum and said the city's resistance was bolstering the defence of all of Ukraine.

Mariupol is a pivotal target in Putin's war -- providing a land bridge between Russian forces in Crimea to the southwest and Russian-controlled territory to the north and east.

- Kyiv regroups -

In the capital Kyiv, a 35-hour curfew came into effect from Monday evening, after Russian strikes laid waste to the Retroville shopping complex, killing at least eight people.

Russia claimed the mall was being used to store rocket systems and ammunition.

Maxim Kostetskyi, 29, a lawyer, said residents were using the "pause" imposed by the lockdown to regroup.

"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.

O.R.Lucchese--INP