James Cleverly told Sky News' Kay Burley the Russian president wanted a "lightning war" to capture Ukraine and quickly install a puppet government, but "that is clearly not working".

'No evidence' Putin will stop - live updates on war in Ukraine

In its morning intelligence update, the Ministry of Defence said reports have suggested Russia may seek to stage a referendum in the captured Ukrainian town of Kherson in an attempt to legitimise the area as a "breakaway republic" - similar to Donbas and Crimea.

It also said Russian forces reportedly fired warning shots at peaceful protesters in Kherson on Monday.

Last week, Russia installed its own mayor in Melitopol after his predecessor was abducted by Russian forces on Friday, and the same has happened in Dniprorudne.

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Russia trying to justify actions

Mr Cleverly added: "It's now quite obvious that Vladimir Putin and the Russian military are attempting some form of legitimacy or justification for their military actions.

"The UK is completely clear: Ukraine is a sovereign territory. They have a right to protect their own borders.

"A faux election to try and justify Russia's aggression to Ukraine will be recognised for exactly what it is. And that is a fake.

"And what we are calling upon Russia to do, what we are calling on Putin to do, is to end this war and end it immediately."

Russians move into Kyiv

There were more explosions in Kyiv overnight as Russian forces moved closer to the Ukrainian capital, with a series of strikes hitting a residential neighbourhood.

Shortly before dawn on Tuesday, the shelling ignited a huge fire and a desperate rescue effort in a 15-storey block of flats. At least one person was killed and others remained trapped inside.

Shockwaves also damaged the entry to a subway station being used as a bomb shelter.

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Mr Cleverly said the targeting of civilians or civilian infrastructure "is a war crime" as he added the situation in Ukraine "is terrible".

"It's obvious that the Russian military are not achieving the goals that they set themselves," he told Sky News.

China must denounce war

He also called on China and "all countries" to denounce Russia's invasion of Ukraine, as he admitted the UK has not had a guarantee from Beijing it will not get involved in the war.

China has been very careful in its response to the invasion, remaining largely silent on the issue.

On Monday, sources in the US government told NBC News that Russia had asked China for military equipment and other support.

The White House is understood to be concerned Beijing may undermine Western efforts to support Ukraine, according to sources cited by The Washington Post and Financial Times.