Russia-Ukraine updates: US to ban Russian carriers from its airspace

As President Vladimir Putin announced his invasion of Ukraine on Russian state TV, President Joe Biden's envoy at the U.N. was making a plea to Moscow to halt any action.

"This is a perilous moment, and we are here for one reason and one reason only: to ask Russia to stop," Ambassador Linda Thomas-Greenfield said at the special session. "Return to your borders. Send your troops, and your tanks, and your planes back to their barracks and hangars. And send your diplomats to the negotiating table."

"Back away from the brink, before it is too late," she added, though it already appears to be too late.

Thomas-Greenfield said she spoke with Biden before Wednesday night's meeting, saying he wanted to make clear the U.S. and its allies "will continue to respond to Russia's actions with unity, clarity and conviction."

Thomas-Greenfield said "all parties are not culpable here. There's no middle ground. ... Russia is the aggressor here."

Like other U.S. officials, and Ukrainian President Volodymyr Zelenskyy, she tried to appeal to the Russian people: "Everyday Russians should be asking themselves, right now, how many Russian lives Putin will sacrifice for his cynical ambitions?"

She ended by quoting the Ukrainian foreign minister, saying, "The people of Ukraine are counting on us. Let’s not let them down."

-ABC News' Conor Finnegan

Explosions have been heard in Kyiv, the capital of Ukraine.

-ABC News’ Kirit Radia

Russian President Vladimir Putin announced that Russia would undertake a special military operation in the Donbas region in eastern Ukraine in a speech on Russian state TV early Thursday morning.

Putin said the operation is aimed at what he called the "demilitarization" and "denazification" of Ukraine.

Putin said Russia’s plans did not include occupying Ukraine, but he called on Ukrainian soldiers to lay down their arms and go home.

He warned outside countries not to interfere.

The U.S., France and other members of the United Nations Security Council are working on a draft resolution to condemn Russia during its late-night session Wednesday, according to France's permanent representative to the U.N.

In somewhat of a rarity, U.N. Secretary-General Antonio Guterres addressed the chamber, speaking to the urgency of the meeting.

Looking directly into the camera ahead of him, Guterres addressed Russian President Vladimir Putin.

"If indeed an operation is being prepared, I have only one thing to say from the bottom of my heart: President Putin, stop your troops from attacking Ukraine. Give peace a chance. Too many people have already died," he said.

Before the meeting, Guterres chatted with Russian Ambassador Vasily Nebenzya, who also talked with China's envoy Zhang Jun.

It's unclear if the resolution will get a vote during the emergency session. But when it comes up, it will likely be denied by Russia and its veto power.

In 2014, after Russia annexed Crimea from Ukraine, a U.S. resolution declaring the action invalid was denied by Russia's veto, while China abstained. The U.S. then brought the resolution to the U.N. General Assembly, where resolutions are non-binding but every member has a vote. It passed with about 100 votes in favor.

-ABC News' Conor Finnegan