Ukraine rejected a Russian ultimatum to surrender the besieged southern city of Mariupol early on Monday, as overnight shelling killed six in the capital Kyiv. US President Joe Biden has meanwhile announced a trip to Poland for crisis talks over the Russian invasion.
Ukraine's Deputy Prime Minister Iryna Vereshchuk dismissed the early morning deadline, saying Moscow should instead allow hundreds of thousands of trapped Mariupol residents to leave the city.
"We can't talk about surrendering weapons," Vereshchuk told the Ukrainska Pravda online newspaper, "we have already informed the Russian side."
The Kremlin's military command warned authorities in Mariupol that they had until 5am on March 21st to respond to eight pages of demands, which Ukrainian officials said would amount to a capitulation.
"We call on units of the Armed Forces of Ukraine, territorial defence battalions, foreign mercenaries to stop hostilities, lay down their arms," said Russian Colonel-General Mikhail Mizintsev, warning those who did not surrender would face court martial, and worse.
Chemical plant targeted
Kyiv's rejection came as Russian bombs hit targets across the country overnight, killing at least six in Kyiv and allegedly damaging a chemical plant in the north of the country causing an "ammonia leakage".
Sumy regional governor Dmytro Zhyvytsky said "Russian artillery shelling" had hit the Sumykhimprom fertiliser plant as he warned residents within a 2.5 kilometres radius to seek shelter.
In Washington, the White House said President Biden -- who is due to visit Europe this week to meet leaders from NATO, the G7 and the European Union -- would also travel to Poland.
He is expected to hold talks with President Andrzej Duda on a joint response to the humanitarian crisis that has seen around two million Ukrainians flee to Poland alone.
Acute humanitarian crisis
The humanitarian crisis is perhaps most acute in Mariupol, where for almost a month Russian forces have bombarded and besieged the southern port city trapping an estimated 350,000 people.
The UN has described the humanitarian situation in the city as "extremely dire" with "residents facing a critical and potentially fatal shortage of food, water and medicines".
Mariupol is a pivotal target in Vladimir Putin's war in Ukraine -- providing a land bridge between Russian forces in Crimea to the southwest and Russian-controlled territory to the north and east.
A Greek diplomat who remained in the city during some of the bombardment said it would rank alongside history's most ruinous wartime assaults.
"Mariupol will be included in a list of cities in the world that were completely destroyed by the war, such as Guernica, Stalingrad, Grozny, Aleppo," Manolis Androulakis said after flying back to Athens.
'The Russians want to exterminate us'
In his latest video address Ukrainian President Volodymyr Zelensky accused Russia of bombarding a Mariupol school sheltering hundreds, calling it an act of "terror that will be remembered even in the next century".
"Russian forces have come to exterminate us, to kill us," he said.
The school attack was the latest potentially devastating strike on a shelter for civilians. Last Wednesday, a theatre where authorities said more than 1,000 people had sheltered was hit, with hundreds still missing in the rubble.
Mariupol officials have said occupying forces have forcibly transported around a thousand residents to Russia and stripped them of their Ukrainian passports -- a possible war crime.
A group of children stuck in a Mariupol clinic for weeks are among those who have been taken to Russian-controlled territory, a carer and a relative of a clinic worker said.
The 19 children, aged between four and 17 and mostly orphans, had been living in freezing cellars hiding from shelling in harrowing conditions.
Zelensky calls for talks
President Zelensky has again suggested that he and Putin hold direct talks.
Authorities in Turkey, where Russian and Ukrainian representatives have been negotiating, said the two sides were close to a deal to stop the fighting.
But the Ukrainian leader appeared to draw some red lines.
"You cannot just demand from Ukraine to recognise some territories as independent republics," he told CNN. "We have to come up with a model where Ukraine will not lose its sovereignty."
