Russian leader Vladimir Putin unleashed a full-scale invasion on Thursday that has killed dozens of people, forced more than 50,000 to flee Ukraine in just 48 hours and sparked fears of a new Cold War in Europe.

Western nations announced personal sanctions targeting Putin as his soldiers were advancing into Ukraine Friday, with Zelensky urging the nation to defend itself.

"This night will be more difficult than the day. Many cities of our state are under attack," Zelensky had said.

"Special attention on Kyiv -- we cannot lose the capital," he said in an earlier address.

"I am turning to our defenders, male and female, on all fronts: this night the enemy will use all the forces it has to crush our defence in a treacherous, harsh and inhumane way," he said.

"Tonight they will attempt a storming" of the capital, he added in an apparent reference to Kyiv.

Zelensky, who earlier called for a stronger response from the West, said he spoke to leaders including French President Emmanuel Macron, German Chancellor Olaf Scholz and US President Joe Biden.

"We have agreed on more aid, more support, significant support for our state," he said.

- 'Point of no return' -

The United States, Canada, Britain and the European Union announced further sanctions against Russia on Friday, including against Putin and his Foreign Minister Sergei Lavrov.

Russia said the sanctions against the pair were "a demonstration of the complete impotence of the foreign policy" of the West.

"We have reached the line after which the point of no return begins," Russian foreign ministry spokeswoman Maria Zakharova said.

Moscow also vetoed -- as expected -- a UN Security Council resolution that deplored "in the strongest terms" Russia's invasion, while China, Indian and the United Arab Emirates abstained.

Putin had earlier described the Ukrainian government as "terrorists" and "a gang of drug addicts and neo-Nazis", urging the country's military to topple Zelensky.

The Ukrainian leader responded by vowing to stay and defend the capital.

"We're all here. Our military is here. Citizens in society are here. We're all here defending our independence, our country, and it will stay this way," Zelensky said in the self-shot video from Kyiv.

The US-led military alliance NATO said it was deploying its rapid response forces for the first time to bolster defences on the alliance's eastern flank.

- Body on the pavement -

Early Saturday, Ukraine's military said on its verified Facebook page that Russia "attacked one of the military units on Victory Avenue in Kyiv. The attack was repulsed," without specifying where exactly the incident took place.

An AFP journalist said there were loud explosions heard in central Kyiv early on Saturday.

Meanwhile, Ukraine's Defence Ministry said early Saturday that "two enemy targets were shot down" -- identifying them as a Russian SU-25 helicopter and a military bomber -- near the separatist zone in the east.

A Russian transport plane had also been "knocked down" near Vasylkiv city, roughly 30 kilometres (19 miles) southwest of Kyiv, the ministry added on its official Facebook page.

Earlier, small arms fire and explosions were heard in the capital's northern district of Obolonsky as what appeared to be an advance party of Russia's invasion force left a trail of destruction.

AFP saw a dead man in civilian clothes lying sprawled on the pavement as nearby medics rushed to help another man whose car was crushed by an armoured vehicle.

In the city centre, soldiers manned intersections around the government district.

Kyiv said that 137 people, including soldiers and civilians, have been killed.

Ukrainian forces reported fighting with Russian armoured units in two locations between 40-80 kilometres north of Kyiv.

The Ukrainian defence ministry urged "citizens to inform us of troop movements, to make Molotov cocktails, and neutralise the enemy".

The ministry said that 2,800 Russian soldiers had been killed, without providing evidence. Moscow has yet to report on casualties.

- 'Not real diplomacy' -

Lavrov said Moscow was ready to talk but only if Ukraine's armed forces "lay down their arms", adding that "nobody intends to occupy Ukraine".

A Kremlin spokesman said Putin was ready to send a delegation to Belarusian capital Minsk "for talks with a Ukrainian delegation".

But the US swiftly dismissed the offer.

After invading Ukraine, "now we see Moscow suggesting diplomacy take place at the barrel of a gun. This is not real diplomacy," State Department spokesman Ned Price said.

The UN said that more than 50,000 Ukrainians had fled the country in the past two days, calling for "safe unimpeded access" for aid operations.

Streams of people in cars and on foot were seen crossing into Hungary, Poland and Romania while hundreds camped out in a train station in the Polish border city of Przemysl.

About 100,000 people are believed to be internally displaced, and in Kyiv, many residents fled their homes and took shelter in the city's subway system.

- 'Harshest' EU sanctions -

The EU on Friday added Putin and Lavrov to the bloc's list of sanctions, in what foreign policy chief Josep Borrell called the "harshest" package ever drawn up by the bloc.

The UK government soon followed suit, ordering all assets of both men frozen.

The United States and Canada will also impose sanctions on the pair, with Washington including a travel ban.

Despite Zelensky calling on Western allies to expel Moscow from the SWIFT banking transfer system, numerous EU countries, including Germany, Hungary and Italy, have been reluctant over fears Russia could cut off gas supplies.

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