Ukraine’s leader has said a “new iron curtain” is falling and closing Russia off from the “civilised world” after it invaded its neighbour. 

Wearing a military uniform, Volodymyr Zelensky addressed the nation as Russia continued its attack on several fronts, moving closer to the capital.

Exact casualty numbers are unclear, but include Ukrainian civilians.

UN estimates suggest that more than 100,000 people have already fled from their homes.

Thousands have crossed into Moldova and Romania. 

“What we have heard today are not just missile blasts, fighting and the rumble of aircraft. This is the sound of a new iron curtain, which has come down and is closing Russia off from the civilised world,” Mr Zelensky said in his video address. 

“Our task is for that curtain not to fall on Ukrainian territory,” he added.

The iron curtain refers to the division between Europe’s communist East and capitalist West from the end of the Second World War to the end of the Cold War. 

Russia’s invasion by land, air and sea began after a pre-dawn TV address where President Vladimir Putin demanded that Ukraine’s military lay down its arms. He threatened any country that attempted to intervene with “consequences you have never seen”. 

It followed weeks of escalating tensions, as Russia massed troops along Ukraine’s borders.

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Mr Zelensky claimed Ukrainian forces had been successfully defending the eastern Donbas region, but said the most problematic area was Kherson in the south of the country, where Russian troops have moved north from annexed Crimea.

Fierce fighting has broken out at an airbase on the outskirts of Kyiv, as government forces try to recapture an airbase and airport after Russian troops took control of it. It is understood to be the closest that Russian forces have managed to get to the Ukrainian capital on the first day of their invasion.

There is also fighting around the site of the former nuclear power plant in Chernobyl. Ukrainian presidential adviser Mykhaylo Podolyak said the nuclear site itself had been lost following a “fierce battle”.

A video, verified by the BBC, appears to show Russian tanks stationed outside the former nuclear power station.

The UK’s Ministry of Defence said Ukrainian forces were putting up “a staunch resistance” to the invasion but that “heavy casualties” had been suffered by both sides. 

This includes six civilians reported to have died in an air strike in Brovary near the capital Kyiv, and a man killed in shelling outside the major north-eastern city of Kharkiv.

Ukraine said it had killed 50 Russian troops and shot down six Russian aircraft, but this has not been verified.

In his video address on Thursday, Mr Zelensky acknowledged that Ukraine had “suffered troop losses” but said “some Russian fighters” had also been captured.

In Kyiv, home to almost three million people, warning sirens have been blaring out as traffic queues to leave the city and crowds seek shelter in metro stations.

“We don’t understand what we should do now,” one woman called Svetlana told the BBC. “We’re now going to a place where we can be safe and we hope we can leave safely.”

Several neighbouring countries have begun preparations to take in a large number of refugees. Moldova alone said more than 4,000 people had come over the border.

The UK, EU and other Western allies have vowed to impose tough new sanctions to punish Moscow, but say they will not send in troops. 

France’s President Emmanuel Macron said the attack would have “deep, lasting consequences for our lives”.

British Prime Minister Boris Johnson and US President Joe Biden announced asset freezes on Russian banks, among other measures. 

Mr Biden said the Russian president had a “sinister vision” for the world. 

For more on this story go to: BBC