full-blown Russian invasion could cause massive casualties and topple Ukraine’s democratically elected government. (AP)

Russian President Vladimir Putin has announced a military operation in Ukraine and warned other countries that any attempt to interfere with the Russian action would lead to “consequences they have never seen.”

He said the attack that began on Thursday was needed to protect civilians in eastern Ukraine – a claim the US had predicted he would falsely make to justify an “invasion”

In a televised address, Putin accused the US and its allies of ignoring Russia’s demand to prevent Ukraine from joining NATO and offer Moscow security guarantees. He said Russia’s goal was not to occupy Ukraine.

US President Joe Biden denounced the “unprovoked and unjustified” attack on Ukraine and said the world will “hold Russia accountable.”

As Putin spoke, big explosions were heard in Kiev, Kharkiv, and other areas of Ukraine.

Putin asks Ukrainian soldiers to lay down arms

A full-blown Russian invasion could cause massive casualties and topple Ukraine’s democratically elected government.

And the consequences of the conflict and resulting sanctions levied on Russia could reverberate throughout the world, affecting energy supplies in Europe, jolting global financial markets and threatening the post-Cold War balance on the continent.

Putin said the Russian military operation aims to ensure a “demilitarisation” of Ukraine. Putin urged Ukrainian servicemen to “immediately put down arms and go home.”

Putin announced the military operation after the Kremlin said rebels in eastern Ukraine asked Russia for military assistance to help fend off Ukrainian “aggression.”

The announcement immediately fueled fears that Moscow was offering up a pretext for war, just as the West had warned.