Moscow: Russian President Vladimir Putin has announced a special "military operation" to protect Donbas, the separatist-held region in eastern Ukraine, media reports said on Thursday.

Delivering an emergency address, Putin said the operation has been launched to demilitarize the country.

This comes hours after Ukrainian President Volodymyr Zelenskyy said Ukraine has not posed and will not pose a threat to Russia.

In an emotional appeal delivered largely in Russian, Zelenskyy said "You are being told that Ukraine can pose a threat to Russia.

"It was not like this in the past, it is not like this now and it will not be so in the future. You demand security guarantees from NATO. We also demand guarantees of our security - from you, from Russia, and other guarantors of the Budapest memorandum," Zelenskyy said in a video address.

Ukrainian President also refuted Moscow's claims that his country poses a threat to Russia and warned that a Russian invasion would cost tens of thousands of lives.

The White House warned on Wednesday that Putin will face significant consequences if Moscow invades Ukraine.

Meanwhile, an emergency session of the UN Security Council on the prevailing situation in Ukraine is underway.

Ukraine requested an urgent United Nations Security Council (UNSC) Meet after Heads of the Ukraine breakaway regions, Donetsk and Luhansk, have asked the Russian President for help.

Putin has also ordered the sending of the Russian Armed Forces to Ukraine's breakaway regions.

Meanwhile, the Ukrainian parliament, Verkhovna Rada, approved declaring a state of emergency in the whole country except for Donetsk and Luhansk regions amid the escalating situation at the country's borders.