Western allies have sought to stage a show of unity as Russian forces close in on Kyiv amid fears a European capital is about to be engulfed in a devastating conflict.

The UK, US and the European Union announced plans to impose personal sanctions on President Vladimir Putin and his foreign minister Sergei Lavrov in response to the Kremlin assault on Ukraine.

As Ukrainians continued to flee across the borders, Boris Johnson said he would be bringing forward measures “imminently”, while the White House and Brussels said they will freeze the assets of the two Russians.

Britain said that it was also extending a ban of Aeroflot flights landing in the UK to cover Russian private jets favoured by Moscow’s oligarchs.

At a meeting of the United Nations Security Council in New York, Russia – as expected – used its veto to block a motion calling for Moscow to cease the attack and withdraw its troops.

However there was disappointment in Western capitals that India and the United Arab Emirates joined China in abstaining, weakening the international show of opposition to Russia’s actions.

And despite escalating economic measures, there was no sign they were having any impact on Mr Putin’s determination to pursue his military offensive against his neighbour which began on Thursday.

Western officials expressed concern that Russia could deploy devastating thermobaric weapons, amid signs that its advance had been slower than planned in the face of stiff Ukrainian resistance.

The so-called “vacuum bombs” suck in oxygen to create powerful, high-temperature explosions which can damage internal organs.

“My fear would be that if they don’t meet their timescale and objectives, they would be indiscriminate in their use of violence,” one official said.

The latest intelligence update from the Ministry of Defence in London said Russian forces had made advances throughout Friday – with a probable amphibious landing in southern Ukraine around Mariupol.

However the primary target remains Kyiv, with Russian forces advancing on “multiple axis” in an attempt to encircle the city.

With reports of sporadic fighting in the suburbs, there are fears of heavy civilian casualties as the main body of Russian troops reach the capital.

Britain’s Chief of Defence Intelligence, Lieutenant General Sir Jim Hockenhull, said their objective was to “secure control of the population and change the regime”.

After President Putin appealed to Ukrainian troops to rise up against their leaders and cease fighting, Mr Johnson issued his own appeal to the Russian people.

In a video posted on social media, he warned their country faced “complete isolation” as a result of their leader’s “needless and bloody war” which would mean many Russian soldiers “will never see their families again”.

Speaking briefly in Russian, he said: “I do not believe this war is in your name.”

At a virtual summit of Nato leaders on Friday, they agreed to send elements from the alliances 40,000-strong response force to protect members states in the east amid fears they could be the next target of Russian aggression.

Nato secretary general Jens Stoltenberg said it was clear the Kremlin’s objectives were “not limited to Ukraine” and that they would “do what it takes to protect and defend every ally and every inch of Nato territory”.

“We are facing a new normal in European security where Russia openly contests the European security order and uses force to pursue its objectives,” he said.