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.

UN Secretary General Antonio Guterres has issued a plea to President Putin calling on him to "give peace a chance".

Putin adds that clashes between Ukrainian and Russian forces are “inevitable” and “only a question of time”.

Only minutes earlier, the UN's under secretary had warned that a military escalation would lead to "an unacceptably high cost, human suffering and destruction".

Putin also says "justice and truth" are on the Russian side, warning that Moscow's response will be "instant" if anyone tries to take on Russia.

The Russian president also says his country's actions are self-defence and tells Ukraine’s military their fathers and grandfathers did not fight so they could help neo-Nazis.

The BBC's Eastern Europe correspondent Sarah Rainsford, who is in the Donetsk region of eastern Ukraine, says she just heard a loud explosion.

In a televised address on Thursday morning, Putin urges Ukrainian soldiers in the combat zone in eastern Ukraine to lay down weapons and return to their homes.

He warned Ukraine that it would be blamed for any bloodshed.

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.

Flights of civilian aircraft in Ukraine's airspace are now "restricted due to potential hazard for civil aviation", according to a Notice to Airmen (Notam) issued on Thursday morning, Flightradar24 data tracking website has said.

No more details were immediately available.

Ukraine's authorities have not commented on the issue.

Meanwhile, arrivals and departures at several key Ukrainian airports appear to be running as scheduled.

Image source, Flightradar24

UN Secretary General Antonio Guterres has been speaking at the emergency meeting of the security council, issuing a direct plea to Russia's president.

He asks Vladimir Putin to stop his troops from attacking Ukraine and urges him to give peace a chance.

The UN has begun another late-night emergency meeting of the security council in New York. It’s 21:40 there which is 04:40 in Ukraine.

It’s the second emergency session in three days – and comes at the request of Ukrainian President Zelensky, who says a Russian invasion is imminent.

The council meeting comes after the Kremlin claimed separatists in the breakaway regions of eastern Ukraine had called for military help from Russia, accusing Ukraine of "aggression".

Diplomats are aiming to pass a resolution condemning Russia for its recent Ukraine actions - but such a resolution will likely fail, as Russia is a permanent member of the UN security council and has veto power.

Still, a large majority of nations condemned Russia's actions at a General Assembly meeting on Wednesday.

You can watch the security council meeting here, external.

Image source, Getty Images

The European Union has released a list of senior Russian officials on whom it has imposed sanctions.

It includes Russia's Defence Minister Sergei Shoigu, and Economy Minister Maxim Reshetnikov.

The Commander-in-Chief of the Russian navy is on the list, as well as the Commander-in-Chief of Russian ground forces.

The EU also sanctioned Margarita Simonyan, editor-in-chief of the English language television news network RT (Russia Today).

You can see the full list here, external.

Airlines should stop flying over any part of Ukraine because of the risk of planes being shot down in error, or a cyber attack targeting air traffic control, a conflict zone monitor says.

The group, Safe Airspace, was set up to give airlines safety information after a passenger plane - Malaysia Airlines flight MH17 - was shot down over eastern Ukraine in 2014.

Safe Airspace has increased its risk level to "do not fly".

Its website reads: "Regardless of the actual movements of Russian forces into Ukraine, the level of tension and uncertainty in Ukraine is now extreme. This itself gives rise to significant risk to civil aviation."

It's being widely reported that US Secretary of State Antony Blinken said he believed that before the night is over, Russian forces will have invaded Ukraine.

Those words were technically put to him by NBC Nightly News anchor Lester Holt - but he did agree with them.

Here's a transcript:

Lester Holt: "Do you have reason to believe that before this night is over, Russian forces will be engaged in something akin to a full invasion of Ukraine?"

Antony Blinken: "I do. 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."

Holt: "To be clear, you think tonight that could happen or will happen?"

Blinken: "Look, I can't put a date or an exact time on it but everything is in place for Russia to move forward."

The crisis has prompted the US and European allies to impose sanctions on some Russian banks and citizens.

But China - a longtime Russian ally - is refraining from following suit.

Our Asia Business Correspondent Mariko Oi explains the scale of China's economic ties with both Russia and Ukraine - and how China could possibly help out Russia.

You can also read more about what China wants from the Ukraine crisis here.

Russia has now issued a civil aviation notice, warning that it is closing virtually all of eastern Ukrainian airspace on the border with Russia, a monitoring group says.

The Open Source Intelligence Monitor says no "limit or ending time" has been provided so far by Moscow in its Notice to Airmen (Notam).

Russian-backed rebels say tens of thousands of people have left Donetsk and Luhansk to cross into southern Russia.

Families making the journey spoke to the BBC about their experiences, with some saying they had not received the food and accommodation they had been promised.

Last week, a Russian-backed separatist leader accused Ukraine of planning an imminent offensive and ordered an evacuation of civilians from Donetsk and Luhansk.

Ukraine said no offensive was planned and it later emerged that the video in which the order was announced had been recorded two days earlier.

Image source, Reuters

US Secretary of State Antony Blinken has 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.

Image source, Getty Images

Just in: the United Nations Security Council will gather at 21:30 local time in New York City (02:30 GMT) on Wednesday to discuss the Ukraine crisis.

One small problem for Western nations - Russia currently holds the rotating presidency of the UN Security Council this month.

The Security Council has four other members: China (a Russian ally), France, the UK and the US.

UN Secretary General António Guterres told a General Assembly session on Ukraine earlier in the day that the world was facing a "moment of peril".

“It is time for restraint, reason and de-escalation. There is no place for actions and statements that would take this dangerous situation over the abyss,” he said, calling for an immediate ceasefire in eastern Ukraine.

Image source, Atif Choudhury

Some British citizens are still desperately trying to get their families out of Ukraine.

Atif Choudhury, from London, says his "stress levels are through the roof" as he tries to get a visa for his Ukrainian fiancee to travel to the UK.

"We're starting to get pretty scared now and I don't know what to do," he tells the BBC.

"The situation has really become unbearable. Emotionally, mentally it's really draining."

Read more:

Ukraine crisis: The Brits trying to get family out of the country

Zelensky also issued a warning to Russians: "If they attack, if they try to take our county - our freedom, our lives, the lives of our children - we will be defending ourselves.

"As you attack, it will be our faces you see, not our backs," the Ukrainian president added.

This speech was Zelensky's last-ditch plea, urging the Russian people to stop their president from launching a devastating war on Ukraine, tweeted the BBC's Eastern European correspondent Sarah Rainsford.

"He was clear. It will mean death. Blood. 10s of 1000s of lives. Russians must know the truth: that you need to stop before it's too late," our correspondent wrote.

"The idea that this war is even possible is something no Ukrainian wanted to believe. But I can't think many are sleeping tonight," she added.