San Francisco Frontiers - European leaders in defiant Kyiv trip as Russia presses in

As talks ground on between Moscow and Kyiv in a bid to halt the devastation, the White House upped the ante by announcing President Joe Biden will visit Europe next week to shore up NATO's unity as war rages on its eastern flank.

The nearly three-week-old conflict has revived Cold War-level tensions between Moscow and the West and sent more than three million Ukrainians fleeing across the border to seek refuge in neighboring states.

Mixed messages have emerged from the latest round of negotiations, with both Moscow and Kyiv signalling progress, but a Ukrainian presidential aide, Mykhailo Podolyiak, cautioning late Tuesday that while "compromise" was possible, "fundamental contradictions" remained.

On the ground in southern Ukraine the presidency reported a humanitarian breakthrough of sorts, with some 20,000 residents evacuating from the besieged port city of Mariupol where there is a critical lack of food, water and medicine.

But Russia extended its military onslaught elsewhere, including a huge strike on an airport in the country's east, while four people were killed in strikes on homes in the capital.

As a 35-hour curfew came into force in Kyiv, President Volodymyr Zelensky hosted the Polish, Czech and Slovenian prime ministers in the first visit by foreign leaders to the besieged city since Russia's invasion.

"We have to halt this tragedy unfolding in the East as quickly as possible," Polish Prime Minister Mateusz Morawiecki said in a Facebook post announcing his arrival, along with Czech premier Petr Fiala and Slovenia's Janez Jansa.

Zelensky earlier addressed a key concern used by Vladimir Putin to justify the invasion of Russia's ex-Soviet neighbour, by saying Ukraine should accept that it would not become a member of the NATO military alliance.

"We have heard for years that the doors were open, but we also heard that we could not join. It's a truth and it must be recognised," Zelensky, who has repeatedly pressed for Ukraine to be allowed into NATO, told military officials.

But in a virtual address to Canadian lawmakers, Zelensky pleaded once again for help from NATO nations to establish a no-fly zone to prevent Russian fighters from achieving superiority in Ukraine airspace.

The appeal has so far not swayed Western nations, who fear the move could trigger a catastrophic escalation of war with nuclear-armed Russia. Zelensky made his disappointment clear.

"How many more of those missiles have to fall on our cities until you make this happen?" he asked.

Zelensky has another opportunity to press his case Wednesday, when he addresses the US Congress by videolink.

- Daring visit -

The bold visit by European leaders -- acting as representatives of the European Union -- came as Moscow faced a new wave of sanctions including higher UK tariffs on Russian vodka and steel, and EU bans on the exports to Russia of champagne and high-end cars.

In a response to the barrage of Western sanctions, Moscow announced that Biden, Canadian Prime Minister Justin Trudeau and top officials from both countries had been hit with measures ensuring "reciprocity".

And Russia retreated one step further from the West by announcing it was abandoning the Council of Europe after pressure mounted for it to be expelled from the pan-European rights body.

According to the United Nations, nearly 1.4 million children have fled Ukraine since the conflict began on February 24 -- almost one child per second. The UN High Commissioner for Human Rights has reported 1,834 civilian casualties.

- 'Are you alive?' -

Surrounded by Russian troops to the north and east, Ukraine's capital has been transformed into a war zone, with apartment blocks badly damaged by bombardment and half of its 3.5 million people now gone.

But Mykola Vasylinko, 62, said despite the curfew and the strikes on Kyiv, it was better than where he had come from, the northern city of Chernigiv which has been relentlessly bombarded.

"This is no Chernigiv, which they try to erase from the earth's surface," he said.

Four large blasts were heard from central Kyiv early Tuesday, sending columns of smoke skyward.

Fire swept through a 16-storey housing block, smoke billowing from the charred husk.

Another residential building in the city's Podilsk area also came under attack.

"At 4:20 am everything was very thunderous, crackling. I got up, my daughter ran to me with a question: 'Are you alive?'," Lyubov Gura, 73, told AFP.

- 'Massive destruction' -

Fox News announced Tuesday that one of its cameramen, Pierre Zakrzewski of Ireland, and a Ukrainian producer, Oleksandra Kuvshynova, were killed when their vehicle was struck by incoming fire in Horenka, outside the capital, a day earlier.

The news came after the Ukrainian parliament's human rights chief said three other journalists had been killed since the invasion began, including a US reporter shot dead Sunday in Irpin, also on the capital's outskirts.

Overnight, Russian shelling also caused massive damage at the airport in the eastern city of Dnipro, authorities said.

"Two strikes. The runway was destroyed. The terminal is damaged. Massive destruction," said regional governor Valentin Reznichenko.

An AFP team saw large plumes of black smoke spewing out of the airport site but could not get closer as it was cordoned off by soldiers, who said the airport could be bombed again.

- Biden to Europe -

Outwardly, at least, the two sides are still far apart in negotiations, with Moscow demanding Ukraine turn away from the West and recognise Moscow-backed breakaway regions.

Ukraine is pushing for a ceasefire and Russian troop withdrawal. On Tuesday, Zelensky sounded a note of cautious optimism about ongoing peace talks and claimed Russia was realising victory would not come on the battlefield.

"They have already begun to understand that they will not achieve anything by war," Zelensky said.

Russia's military progress has been slow and costly, with Moscow apparently underestimating the strength of Ukrainian resistance.

Western defence experts believe Russia's military now needs time to regroup and resupply its troops, suggesting a possible pause or slowdown in fighting.

In that context, Biden will use a trip to an emergency NATO summit next week to demonstrate Washington's "iron-clad" backing for its allies, the White House said, also attending an EU summit in Brussels to discuss the invasion.

NATO worries that Russia is gearing up to carry out a chemical attack in Ukraine, secretary general Jens Stoltenberg said, citing "absurd claims" that Ukraine possesses biological weapons labs and warning that Russia would pay "a high price" if it did so.

On Tuesday, Chinese Foreign Minister Wang Yi warned Beijing did not want to be impacted by Western sanctions on Russia, as US pressure grows on Beijing to withdraw support from Moscow.

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C.Lewis--SFF