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The UN chief made an impassioned, personal plea for peace to Russian President Vladimir Putin on Wednesday, even as Moscow began its all-out assault on neighbouring Ukraine.
"President Putin, stop your troops from attacking Ukraine", UN Secretary General Antonio Guterres said at an emergency UN Security Council session. "Give peace a chance, too many people have already died."
But it was too late.
In an address on Russian state TV, broadcast at the same time as the UN Security Council began its emergency meeting in New York late on Wednesday, Mr Putin announced his military operation in eastern Ukraine. Russian forces fired missiles at several Ukrainian cities and landed troops on its south coast.
"At the exact time as we are gathered in the council seeking peace, Putin delivered a message of war in total disdain for the responsibility of this Council. This is a grave emergency," US Ambassador Linda Thomas-Greenfield told the council.
The Ukraine reached a breaking point after pro-Russian separatists who partially control regions in eastern Ukraine requested Russians help to address what they called Ukrainian "aggression".
"Russia's attack on Ukraine is tantamount to an attack on the UN and every member state in the chamber tonight," Ms Thomas-Greenfield said.
Ukraine's President Volodymyr Zelenskyy issued a video statement saying that Russian leadership had approved an offensive, and that President Vladimir Putin rejected a plea for peace talks.
Earlier on Wednesday, Foreign Minister Dmytro Kuleba along with the the UN chief told the General Assembly in New York said a full-scale invasion of Ukraine would unleash a wave of devastation with far-reaching global consequences.
Wednesday's warnings came as Ukraine imposed a month-long state of emergency starting on Thursday and the country announced a mobilisation of reservists a day after Russia recognised two breakaway enclaves in the east.
“We need swift, concrete and resolute actions and new type of actions by the United Nations and international community, which is relevant to the level of the threat we all, not just Ukraine, face today because of Russia's aggressive course,” said Mr Kuleba.
UN Secretary General Antonio Guterres called for a ceasefire in eastern Ukraine and said "our world is facing a moment of peril" over the crisis.
"If the conflict in Ukraine expands, the world could see a scale and severity of need unseen for many years," Mr Guterres said.
Pentagon spokesman John Kirby said the Russian force of more than 150,000 troops arrayed along Ukraine’s borders is in an advanced state of readiness.
“They are ready to go right now,” Mr Kirby said.
In addition to the 30-day state of emergency, Ukraine's government has announced compulsory military service for all men of fighting age.
The UN meeting came as Ukraine's parliament, cabinet and foreign ministry websites went down in the latest apparent cyber attack. Government websites have experienced several outages in recent weeks.
Western powers have slapped sanctions on Moscow over its decision to send troops into rebel-held, pro-Moscow regions of Europe's second-largest country.
The sanctions are designed to increase with each Russian push into Ukraine, but critics say the measures don't go far enough.
On Wednesday, President Joe Biden announced sanctions on the Nord Stream 2 pipeline after co-ordinating with German Chancellor Olaf Scholz, who has said the Russia-German gas duct would not become operational for now.
“These steps are another piece of our initial tranche of sanctions in response to Russia’s actions in Ukraine,” Mr Biden said in a statement. “As I have made clear, we will not hesitate to take further steps if Russia continues to escalate.”
Mr Kuleba compared Russia’s aggression and military build-up in Eastern Europe to the crises on the continent ahead of the outbreaks of the First and Second World Wars.
The world body had one “last chance” to deter Russian President Vladimir Putin from launching a “large scale war in Ukraine” that would cause widespread suffering and signal the “end of the world order as we know it”, Ukraine's top diplomat warned.
“This is a grim scenario which will throw us back to the darkest times of the 20th century," Mr Kuleba said.
"Russia will not stop at Ukraine. If a permanent member of the UN Security Council succeeds in breaking literally all rules, other actors will be inspired by him and follow his pattern."
Russia’s UN ambassador defended his government’s decision to recognise the independence of Ukraine’s breakaway regions, saying Moscow was sticking up for the rights of millions of Donbass residents.
Vassily Nebenzia said the people in the pro-Moscow separatist regions of Donetsk and Lugansk were “fully within their rights to consider themselves independent” from the rest of Ukraine and were now under Russian protection.
"Our country could not remain indifferent to the fate of the four million people of Donbas," Mr Nebenzia said.
Mr Kuleba urged UN members to not recognise Ukraine’s pro-Moscow breakaway regions as independent. But he was short on detail of what actions the UN should take against Russia, which as a permanent UN Security Council member can veto any major decisions.
Mr Guterres said an escalation of the conflict would lead to humanitarian suffering on “a scale and severity of need unseen for many years” and that UN monitors would keep track of abuses against civilians in the turbulent region over the coming weeks and months.
“Our Human Rights Monitoring Mission has seven offices throughout the country — on both sides of the contact line — documenting civilian casualties, monitoring freedom of movement, and reporting on allegations of human rights violations,” he said.
The day-long UN meeting was arranged in advance to discuss Russia’s previous incursion into Ukraine in 2014 as well as unresolved issues between Kiev and the separatist-held Donetsk and Luhansk regions.
Mr Putin ordered the deployment of troops to the two breakaway regions after recognising them as independent on Monday, accelerating a crisis that could spiral into Europe’s worst military confrontation in decades.
The Russian leader on Wednesday said Moscow was ready to look for “diplomatic solutions” to tension with the West over Ukraine, but stressed that the country's security interests were non-negotiable.
Russia seized the Crimean Peninsula in 2014 and has backed an insurgency in eastern Ukraine that has claimed more than 13,000 lives. Intense diplomacy is under way to avert an escalation of the eight-year conflict.
Prominent humanitarian Jan Egeland on Wednesday said that aid workers would struggle to cope with the mass displacement resulting from full-blown fighting in Ukraine, a country of about 44 million people
“It would be so utterly insane to launch upon the world another cataclysmic war,” said Mr Egeland, secretary general of the Norwegian Refugee Council and a former UN aid chief.
Aid groups would be overwhelmed by the suffering, especially among the roughly two million people living near the front lines, and “wouldn't even be able to meet a fraction of the needs”, he said.
Agencies contributed to this report.
