Russian President Vladimir Putin must face the “severest consequences” for his “unprovoked aggression” against Ukraine, Nicola Sturgeon has insisted.

The Scottish First Minister spoke out about the “appalling and horrific” developments as Boris Johnson led a crisis meeting of senior ministers and officials to consider how to respond to the military action.

But he insisted that Mr Putin had “chosen a path of bloodshed and destruction” with his attack, pledging that the UK and and its allies would respond “decisively”.

Explosions could be heard in the Ukrainian capital of Kyiv shortly after a televised address from the Russian leader, while explosions were also reported in the cities of Odesa and Kharkiv.

Mr Putin insisted in his address, early on Thursday morning, that his action was in response to threats from Ukraine, claiming that Russia was not seeking to occupy Ukraine and insisting the responsibility for bloodshed lay with the Ukrainian “regime”.

He also warned other countries that any attempt to interfere with the Russian action would lead to “consequences they have never seen”.

Ms Sturgeon tweeted that the overnight developments in Ukraine “however anticipated – are appalling and horrific”.

She stated: “The Kremlin must face the severest consequences for this unprovoked aggression.

“And the world must stand in solidarity with the people of Ukraine.”

On Wednesday Ms Sturgeon met the acting consul general of Ukraine, Yevhen Mankovskyi, and Linda Allison, the chairwoman of the Scottish branch of the Association of Ukrainians in Great Britain.

In the wake of those talks she urged the UK to impose tougher sanctions against Russia, saying while there had been “some very tough rhetoric from Boris Johnson” this now needed to be “matched by action”.

Ms Sturgeon also made clear she was “appalled” at former Scottish first minister and now Alba Party leader Alex Salmond’s continued involvement with Russia Today – the Kremlin-backed TV channel on which he has a television talk show.

The Scottish Parliament will debate the situation this afternoon, and express its solidarity with Ukraine, with a demonstration also planned for outside the Russian Consulate in Edinburgh.

Health Secretary Humza Yousaf meanwhile said that the First Minister had made clear “we stand full square in solidarity with the people, Parliament, the government of Ukraine”.

Speaking on BBC Radio Scotland’s Good Morning Scotland programme he insisted: “Their territorial integrity must be preserved and overnight developments are clearly very, very concerning.

“That’s why we are, I hope in a constructive manner, saying to the UK Government that we need to go further in terms of sanctions.

“We need to make it clear to those people, not just Vladimir Putin but the people around him in the Kremlin, that there are serious consequences when you flagrantly violate international law.”