Russian President Vladimir Putin authorised a special military operation against Ukraine to eliminate what he said was a serious threat against his country, saying his aim was to de-militarise Russia's southern neighbour, the Reuters news agency reported.
Biden said in a statement that Putin "has chosen a premeditated war that will bring a catastrophic loss of life and human suffering."
He added: "Russia alone is responsible for the death and destruction this attack will bring. The world will hold Russia accountable."
Biden declared that the United States would coordinate with its NATO allies "to ensure a strong, united response that deters any aggression against the alliance."
"The prayers of the world are with the people of Ukraine tonight as they suffer an unprovoked and unjustified attack by Russian military forces," he said in a tweet.
"President Putin has chosen a premeditated war that will bring a catastrophic loss of life and human suffering," he added.
'Unprovoked and unjustified Russian attack' on Ukraine: Polish president
Polish President Andrzej Duda tweeted: "Despite the efforts of the international community, Ukraine has fallen victim to a brutal, unprovoked and unjustified Russian attack."
Duda added: "We are working together with our allies from NATO and the EU. We will jointly respond to Russia's brutal aggression and will not leave Ukraine without support."
He said in a separate tweet that Russia's invasion of Ukraine "is an unprecedented violation of international law" and that Russia "has excluded itself from the international community."
"Today at 5:48 a.m. I spoke with Ukrainian President Volodymyr Zelenski," Duda said. "Russia has invaded Ukraine, moving forward with what appears to be a large-scale attack. This is an unprecedented violation of international law. Russia has excluded itself from the international community."
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Source: PAP, Reuters