Russia attacks Ukraine

US President Joe Biden will deliver remarks on Thursday afternoon on Russia's decision to take military action in Ukraine, according to a White House official.

Biden will announce "further consequences the United States and our Allies and partners will impose on Russia for its unprovoked and unjustified attack on Ukraine," said the official.

Shortly after Russian President Vladimir Putin announced the military operation early Thursday morning, Biden released a statement decrying Putin's choice as bringing "a premeditated war that will bring a catastrophic loss of life and human suffering."

An adviser for the Interior Minister of Ukraine, Anton Gerashchenko, said early on Thursday morning that Russia’s “invasion has begun,” with “missile strikes on Kyiv.”

Gerashchenko added on his Facebook page that control centers such as airfields and military headquarters are being hit by the shelling in Kyiv and Kharkiv, and that there is artillery fire along the border.

The Russian ambassador to the United Nations, Vasily Alekseevich Nebenzya, defended Russia's decision to take military action in the Donbas region of eastern Ukraine during an emergency meeting of the UN Security Council.

"The root of today's crisis around Ukraine is the actions of Ukraine itself, who for many years were sabotaging its obligations under the (Minsk agreement)," said Nebenzya. He claimed that the Russian operation aimed to protect residents in the separatist pro-Moscow regions of eastern Ukraine, "who for eight years have been cowering from Ukraine's shelling."

He claimed that "Ukrainian provocation against those in Donbas not only has not stopped but has intensified," which prompted separatist leaders in the regions of Luhansk and Donetsk to request Russian assistance.

The US State Department has warned that Russia may use so-called false flags, including claims that Ukraine is attacking Donetsk, to justify an invasion. 

Europe's top air traffic authority is urgently telling airlines and other civilian flights to stay away from Ukrainian airspace. 

The head of European Organization for the Safety of Air Navigation, better known as Eurocontrol, tweeted early Thursday, "All operators advised."

Eurocontrol Director General Eamonn Brennan said that a Russian notice to pilots published earlier was "likely due to military activity."

Earlier today, Ukrainian authorities issued a notice restricting the country's airspace starting early Thursday morning and lasting until midnight GMT (7 p.m. ET).

The British Ambassador to the United Natiions said Russia has been holding a gun to Ukraine’s head for months and asked Russia, again, to avoid war.

“For months, Russia has been holding a gun to Ukraine’s head. Now, President Putin’s finger is on the trigger,” United Kingdom Ambassador Barbara Woodward said Wednesday night during a special UN Security Council meeting.

“A full-scale conflict in a country of 44 million people will bring immense suffering, casualties on both sides and devastating humanitarian consequences,” she said.

“The world is calling for peace but Russia is not listening,” she added. 

“We’re here for the second time this week in the council,” Woodward said. “My Prime Minister and foreign and defense secretaries have been unsparing in their diplomatic efforts. But we have also announced a significant further sanction step with our allies. A package targeted against some of the Russian oligarchs, banks and politicians supporting President Putin and we will ratchet up economic consequences should Russia continue its aggression.”

“There is still time for restraint, reason and de-escalation but that time is now.”

Russian President Vladimir Putin called for Ukraine's "demilitarization" in televised remarks, shortly after announcing a military operation in the region of Donbas in eastern Ukraine.

"Circumstances require us to take decisive and immediate action," Putin said, according to a RIA-Novosti transcript. "The People's Republics of Donbas turned to Russia with a request for help. In this regard, in accordance with Article 51, part 7 of the UN Charter, with the sanction of the Federation Council and in pursuance of the friendship treaties ratified by the Federal Assembly and mutual assistance with the DPR and LPR, I have decided to conduct a special military operation." 

Putin's remarks came as concerns mounted of an imminent full-scale Russian invasion. Ukrainian President Volodymyr Zelensky said in an emotional speech early Thursday that the Russian leadership had approved military action in Ukraine and vowed the country would defend itself.

CNN teams in the Ukrainian capital Kyiv are hearing explosions come from the east, in the direction of the international airport.

Reports on social media indicate several explosions in the Boryspil area to the east of the capital, where the international airport is located. 

Two people in the Ukrainian city Kramatorsk also told CNN they have heard at least two massive explosions in the early hours of Thursday.

In a statement early Thursday morning, US President Joe Biden condemned Russia's actions, shortly after Russian President Vladimir Putin announced military action in the Donbas region of eastern Ukraine.

Biden's statement:

Biden added that he is monitoring the situation from the White House, and will meet with the other G7 leaders in the morning. He will announce "further consequences" imposed on Russia by the US and its allies tomorrow, he said.

In an early morning address on national television, Russian President Vladimir Putin said: “Our plans are not to occupy Ukraine, we do not plan to impose ourselves on anyone."

Early Thursday morning, Putin said his troops will take military action in Donbas, the area of eastern Ukraine that contains the separatist-held regions of Donetsk and Luhansk which he recognized as independent on Monday.