Moscow/Kiev: Russian President Vladimir Putin on Thursday announced a military operation in eastern Ukraine's Donbas region, which the authorities in Kiev have described as a "full-scale invasion".
Donbas comprises the rebel regions of Luhansk and Donetsk which were declared as independent states earlier this week by the Russian leader which led to widespread condemnation and sanctions against Moscow.
In a televised speech to the nation on Thursday morning, Putin said Russia did not plan to occupy Ukraine, but warned that Moscow's response would be "instant" if anyone tries to take on Russia, the BBC reported.
He said that the Ukrainian people would be able "to choose freely" who runs the country and reiterated that his country's actions were in "self-defence".
The Russian leader urged the Ukrainian soldiers who are facing off Russian-backed rebels to lay down weapons and return to their homes. He also told them that their "fathers and grandfathers did not fight so they could help neo-Nazis".
Putin added that clashes between Ukrainian and Russian forces were "inevitable" and "only a question of time".
Immediately after Putin made the announcement, there were explosions heard in Kiev and also across Ukraine, including towns in the east, like Kramatorsk, close to areas controlled by pro-Russian separatists, said the BBC.
The Russian President's declaration came at the same time as the UN Security Council in an emergency meeting was imploring him to stop pushing more troops towards Ukraine.
In his appeal, UN Secretary-General Antonio Guterres asked Putin to stop the Russian troops from attacking Ukraine and to "give peace a chance" as "too many people have already died.
Meanwhile in Kiev, Ukrainian Foreign Minister Dymtro Kuleba said that Putin has launched a "full-scale invasion of Ukraine".
Taking to Twitter shortly after the announcement, he said: "Putin has just launched a full-scale invasion of Ukraine. Peaceful Ukrainian cities are under strikes. This is a war of aggression.
"Ukraine will defend itself and will win. The world can and must stop Putin. The time to act is now."
In a last ditch appeal before Putin made the announcement, Ukrainian President Volodymyr Zelensky said that Russia could start "a major war in Europe" and urged Russian citizens to oppose it.
Zelensky said Russia had almost 200,000 troops and thousands of combat vehicles on Ukraine's borders, the BBC reported.
Condemning Putin's latest move as "unprovoked and unjustified attack by Russian military forces", US President Joe Biden said that the Russian leader has "chosen a premeditated war that will bring a catastrophic loss of life and human suffering".
In a statement released by the White House, Biden said: "Russia alone is responsible for the death and destruction this attack will bring, and the US and its allies and partners will respond in a united and decisive way.
"The world will hold Russia accountable."
In a tweet, NATO Secretary-General Jens Stoltenberg strongly condemned Russia's "reckless attack" on Ukraine, which puts at risk countless civilian lives.
"This is a grave breach of international law & a serious threat to Euro-Atlantic security. NATO Allies will meet to address Russia's renewed aggression."
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