'Humanitarian catastrophe' is on the horizon for Ukraine according to Britain's UN Ambassador.
Dame Barbara Woodward issued the stark warning at an emergency meeting of the Security Council.
Several members, including Dame Barbara, accused Russia of 'indiscriminate attacks on men, women and children' and violating international humanitarian law.
The meeting was held as Russian continues to invade Ukraine as dozens have already been killed in air strikes.
Dame Barbara said: "As a result of President Putin's decision to launch a full-scale invasion of Ukraine, a country of 44 million people is now on the brink of humanitarian catastrophe.
"Missiles have rained down on Kharkiv, with cluster munitions hitting residential areas and injuring residents. Disruption to supply chains has caused food shortages in Kramatorsk.
"The reckless bombing of an oil depot in Vasylkiv, has unleashed toxic fumes in nearby communities.
"Violence in Kyiv has forced people to seek refuge underground, with many thousands, including the elderly and disabled, unable to evacuate."
The UK permanent representative to the UN told the Security Council that "hundreds of civilians had been killed as a result of the Russian invasion" and seven million people had been displaced, with the figure "rising exponentially".
Ukraine's representative, Sergiy Kyslytsya, told the council that Kyiv was "sitting within Russian crosshairs right now" and that 352 people, including 16 children, had been killed as of Monday in the fighting.
He accused Moscow troops of attacking hospitals and ambulances in a determination to "kill civilians", adding: "There is no debate. These are war crimes."
But Vasily Nebenzya, the Russian UN permanent representative, said his country's armed forces did "not have the goal of occupying Ukraine or harming the local population".
The chief prosecutor of the International Criminal Court said he plans to open an investigation "as rapidly as possible" into possible war crimes and crimes against humanity in Ukraine.
Ukrainian President Volodymyr Zelensky echoed Mr Kyslytsya's statements in a late-night address on Monday. In a video posted to social media, the leader said that in five days Russian forces had launched 56 missile strikes and 113 cruise missiles in Ukraine.
He added: "Today, Russian forces brutally fired on Kharkiv from jet artillery. It was clearly a war crime.
"Kharkiv is a peaceful city, there are peaceful residential areas, no military facilities. Dozens of eyewitness accounts prove that this is not a single false volley, but deliberate destruction of people: the Russians knew where they were shooting."
"There will definitely be an international tribunal for this crime - it's a violation of all conventions. No one in the world will forgive you for killing peaceful Ukrainian people," he said.
It comes as Prime Minister Boris Johnson flies to Nato's border with Russia today, pledging that Vladimir Putin will "feel the consequences" for invading Ukraine.
Boris Johnson will meet counterparts in Poland and Estonia and visit British troops as he pushes for Western unity in punishing the Russian president for starting a conflict that has taken "hundreds" of lives in only five days.
Prior to his trip to eastern Europe, the Prime Minister urged allies to "speak with one voice" to ensure "Putin must fail".
Foreign Secretary Liz Truss is also embarking on a diplomatic mission as she prepares to address the United Nations Human Rights Council in Geneva.
The Cabinet minister is expected to tell the council that Mr Putin has "blood on his hands" and that he has been "murdering Ukrainians indiscriminately".
"Putin is violating international law... he is violating human rights on an industrial scale and the world will not stand for it," Ms Truss is expected to say in a speech urging the West to "isolate" Russia as a result of the war it has instigated.
The comments are due to be made only 24 hours after Moscow suggested it had put the Russian nuclear deterrent on high alert in response to unspecified comments made by Ms Truss.
The ministerial trips come after the UK Government looked to "up the pressure" on the Kremlin on Monday, with fresh sanctions on Russian banks and Transport Secretary Grant Shapps urging all UK ports to deny access to Russian flagged, registered or operated vessels.
Mr Johnson, in a call on Monday with world leaders from the G7, Nato and the European Union, stressed the need for allies to continue to provide Kyiv with defensive weapons.
He also said Ukraine's neighbours would require support to deal with "large numbers of Ukrainians escaping violence".
On Tuesday, the Prime Minister is scheduled to meet with Warsaw and Tallinn leaders and visit British troops serving in Estonia, which shares a border with Russia.
Speaking before his visit to the two Nato members, Mr Johnson said: "Alongside all our international allies the UK will continue to bring maximum pressure to bear on Putin's regime to ensure he feels the consequences of his actions in Ukraine.
"We speak with one voice when we say, Putin must fail."
Officials said Mr Johnson will meet Polish Prime Minister Mateusz Morawiecki before travelling on to Estonia, where he will hold talks with Nato secretary general Jens Stoltenberg.
They will jointly visit British troops serving "on the front line of Russian aggression" in Tapa, No 10 said, before meetings with Estonian Prime Minister Kaja Kallas and Estonian President Alar Karis to discuss security.
Ukraine was braced for another evening of attacks, with reports that Kyiv had come under fire on Monday evening.
BBC broadcaster Clive Myrie said he had to take shelter underground after the building he was reporting from in the capital was "shaken by nearby missile fire".
He tweeted: "Windows shook. Closest blast yet to our base. Fighting coming closer to heart of Kyiv."
It came after a first round of Ukraine-Russia talks aimed at ending the fighting concluded with no immediate agreements.
Western officials believe that so far around half of the Russian forces that had been ringed around Ukraine's borders have been committed to the assault on the country.
Moscow could use more indiscriminate force if the invasion stalls, British officials fear.
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