Russian President Vladimir Putin authorised a special military operation against Ukraine to eliminate what he said was a serious threat against his country, the Reuters news agency reported.
In a tweet early on Thursday, Polish President Andrzej Duda said: "Despite the efforts of the international community, Ukraine has fallen victim to a brutal, unprovoked and unjustified Russian attack."
He 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."
'Unprecedented violation of international law'
Duda 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."
Biden vows 'strong, united response'
US President Joe Biden said in a statement that the world would hold Russia accountable and that the United States and its allies would respond in a united and decisive way to "an unprovoked and unjustified attack by Russian military forces."
Biden declared that the United States would coordinate with its NATO allies "to ensure a strong, united response that deters any aggression" against the Western military alliance.
Source: PAP, Reuters