"I have made the decision of a military operation," Vladimir Putin said  in Moscow.

In an address  on national television,  Putin announced military action in Donbas, urging Ukrainian forces to lay down their arms and go home, according to state-run news agencies RIA-Novosti and TASS.

Putin warned that all responsibility for any potential bloodshed will be on the conscience of the Ukrainian government, and said he was confident Russian service members will fulfill their duty.

Putin earlier had recognized the independence of self-proclaimed Donetsk and Lugansk republics of Ukraine.

According to Sputnik, Putin has directed Russian forces to conduct a special operation in the Donbass region, according to February 24 remarks from the Russian president. Putin declared that he expects consolidated Parliamentary support for the operation in the Donbass region.

Sputnik report said Putin remarked that the NATO-allied war machine supporting 'Neo-Nazis' in Ukraine is moving and closely approaching Russia's borders. He emphasized that Russia, for the past 30 years, has been attempting to negotiate NATO non-expansion to the east, despite being faced with deceit and blackmail.

Responding to Ukrainian President Volodymyr Zelensky's claim that Kiev may reconsider the country's non-nuclear status under the 1994 Budapest Memorandum, Putin declared that Russia would not let such a thing happen, reported Sputnik.

USA REACTS: 

US President Joe Biden called the action an "unprovoked and unjustified attack by Russian military forces".

"The prayers of the entire world are with the people of Ukraine," he said.

"President Putin has chosen a premeditated war that will bring a catastrophic loss of life and human suffering," he said.

He said Russia alone is responsible "for the death and destruction this attack will bring, and the United States and its allies and partners will respond in a united and decisive way."

"The world will hold Russia accountable," said Biden.

He says he will be monitoring the situation from the White House and will meet with G7 leaders in the morning before announcing "further consequences" for Russia.

Biden says there will be a "strong, united response" from Nato allies that deters any aggression against its members.

"Tonight, Jill and I are praying for the brave and proud people of Ukraine," he says.

Moscow had earlier massed more than 100,000 troops near its border with Ukraine and had sent the military personnel to exercises in neighbouring Belarus amid rising fears that it could invade Ukraine any moment.

NATO Reaction:

NATO Secretary General Jens Stoltenberg said: I strongly condemn Russia’s reckless and unprovoked attack on Ukraine, which puts at risk countless civilian lives. Once again, despite our repeated warnings and tireless efforts to engage in diplomacy, Russia has chosen the path of aggression against a sovereign and independent country.

This is a grave breach of international law, and a serious threat to Euro-Atlantic security. I call on Russia to cease its military action immediately and respect Ukraine’s sovereignty and territorial integrity. NATO Allies will meet to address the consequences of Russia’s aggressive actions. We stand with the people of Ukraine at this terrible time. NATO will do all it takes to protect and defend all Allies.

The Conflict:

The present conflict comes nearly eight years after Russia annexed Ukraine's southern Crimea peninsula in 2014 and backed a bloody rebellion in the eastern Donbas region.

Moscow has accused the Ukrainian government of failing to implement the Minsk agreement, which sought to end war in the Donbas region of Ukraine, while the Russian government feared that Ukraine’s membership of the EU and NATO would complete a western wall of allied countries by restricting Russia’s access to the Black Sea.