Explosions in the Ukranian capital Kyiv have just been heard live on air on CNN.
During correspondent Matthew Chance's live broadcast, large bangs resounded in the distance.
BBC's Paul Adams in Kyiv has just reported hearing five to six "distant explosions" in Kyiv, and says there are reports are coming in of explosions elsewhere in the country.
Local media report that gunfire was heard on Thursday near the main airport of Boryspil in Kyiv.
US President Joe Biden has responded to what he calls an "unprovoked and unjustified attack by Russian military forces".
He says "the prayers of the entire world are with the people of Ukraine".
"President Putin has chosen a premeditated war that will bring a catastrophic loss of life and human suffering," he says.
"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."
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.
Earlier, Russian President Vladimir Putin has just announced a "military operation" in Ukraine's Donbas region.
He made the declaration in a televised speech at the same time as the UN Security Council was imploring him to stop.
Ukraine’s parliament and other government and banking websites were hit with another punishing wave of distributed-denial-of-service attacks Wednesday, and cybersecurity researchers said unidentified attackers had also infected hundreds of computers with destructive malware.
Earlier, separatists in Ukraine asked Moscow to help repel "aggression" on Wednesday and explosions rocked the breakaway eastern city of Donetsk as the United States warned everything is in place for a major attack by Russia on its neighbor.
A short time later, the Ukrainian president rejected Moscow’s claims that his country poses a threat to Russia and said a Russian invasion would cost tens of thousands of lives.
“The people of Ukraine and the government of Ukraine want peace,” President Volodymyr Zelenskyy said in an emotional overnight address, speaking in Russian in a direct appeal to Russian citizens. “But if we come under attack, if we face an attempt to take away our country, our freedom, our lives and lives of our children, we will defend ourselves. When you attack us, you will see our faces, not our backs.”
Zelenskyy said he asked to arrange a call with Russian President Vladimir Putin late Wednesday, but the Kremlin did not respond.
As world leaders waited to see if Russian President Vladimir Putin would cast the die and order troops deeper into Ukraine, they worked to maintain a united stance and vowed to impose tougher sanctions in the event of a full-fledged invasion.
And the United Nations Security Council quickly scheduled an emergency meeting Wednesday night at Ukraine’s request.
After weeks of rising tensions, Putin’s steps this week dramatically raised the stakes. He recognized the independence of the separatist regions, a move he said extends even to the large parts of the territories now held by Ukrainian forces, and had parliament grant him authority to use military force outside the country.
Putin laid out three conditions that he said could end the standoff, urging Kyiv to renounce its bid to join NATO, to partially demilitarize and to recognize Russia’s sovereignty over Crimea, the Black Sea peninsula that Moscow annexed from Ukraine in 2014. Ukraine long has rejected such demands.
US BELIEVES WAR IS IMMINENT
US Secretary of State Antony Blinken told NBC News, "Unfortunately, Russia has positioned its forces at the final point of readiness across Ukraine's borders to the north, to the east, to the south. Everything seems to be in place for Russia to engage in a major aggression against Ukraine."
America's top diplomat also denied Washington was out of options to deter Russia. "I think [there’s] still an opportunity to avert a major aggression, although again, they're in their final stages of being able to engage in one.
"We said very clearly that if Russia continues to escalate, so will we. And so they have to factor that in to what they're thinking.
"At the end of the day, if that doesn't stop President Putin, we've made very clear along with all of our allies and partners that there will be massive consequences going forward, a price that Russia will have to pay for a long, long time," Blinken added.
RUSSIA PREPARES FOR WAR
Russia has evacuated its embassy in Kyiv and marked Defender of the Fatherland Day, a holiday high in national symbolism. Along the Kremlin wall, soldiers put red carnations on the Tomb of the Unknown Soldier while Putin honored the memory of the ones who died in past wars.
Putin whipped up Russian nationalism on Monday with a fiery speech indicating that Ukraine historically had no cause for being. He said during Wednesday’s commemoration that Russia would continue to strengthen and modernize its army and navy, “striving to increase their effectiveness, so they are fitted out with the most cutting-edge equipment.”
UKRAINE AIRSPACE CLOSED
Airspace over all of Ukraine has been shut down to civilian air traffic, according to a notice posted to air crews early Thursday.
A commercial flight tracking website shows that an Israeli El Al Boeing 787 from Tel Aviv to Toronto turned abruptly out of Ukrainian airspace before detouring over Romania, Hungary, Slovakia and Poland.
The only other aircraft tracked over Ukraine is a U.S. RQ-4B Global Hawk unmanned surveillance plane that began flying eastward early Thursday after Russia put in place flight restrictions over Ukrainian territory.
UN SECURITY COUNCIL CONVENES
The U.N. Security Council has scheduled an emergency meeting Wednesday night at the request of Ukraine, which says there is an immediate threat of a Russian invasion.
The meeting comes two days after the 15-member council held an emergency open meeting also requested by Ukraine. That session saw no support for Russian President Vladimir Putin’s declaration of independence for two separatist areas in Ukraine’s east and his announcement that Russian troops would be heading there to keep the peace.
The meeting Wednesday night comes as council diplomats are finalizing a draft resolution that they say would make clear that Russia is violating the U.N. Charter, international law and a 2015 council resolution endorsing the Minsk agreements aimed at restoring peace in eastern Ukraine.
They say the resolution would urge Russia to get back into compliance immediately.
UN Secretary General Antonio Guterres spoke at the emergency meeting of the security council, issuing a direct plea to Russia's president.
He asked Vladimir Putin to stop his troops from attacking Ukraine and urges him to give peace a chance.
