AS I write, 130,000 Russian troops are amassed on the Ukrainian border.
The deployment is undoubtedly the biggest ever demonstration of Russian hostility towards Ukraine — it dwarfs the 30,000 troops Russia sent to annex Crimea in 2014.
A month ago President Putin made Nato an offer — he would withdraw his troops and his threats if the alliance conceded to his demands.
Russia’s price? A guarantee that the people of Ukraine would never be allowed to exercise their sovereign right to join Nato and that the entirety of Eastern Europe would never again be able fully to defend itself.
A further Russian invasion of Ukraine would be a political and humanitarian disaster. Our response will be judged by Ukraine and by the world.
Since the invasion of Crimea we have trained more than 21,000 Ukrainian military personnel and provided £2.2million of military equipment.
Two weeks ago we sent anti-armour weaponry to Ukraine to strengthen their defences further.
We are also preparing a package of sanctions and other measures which would be enacted the moment the first Russian toecap crosses further into Ukraine.
And today I have committed an unprecedented package of support to Nato’s eastern flank.
Land, sea and air from Cyprus in the south to Estonia in the north will be guarded by the British Armed Forces.
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We have done all this not as a show of hostility towards Russia but as a demonstration that we will always stand up for freedom and democracy in the face of aggression.
Our preference is, and will remain, to resolve this diplomatically.
That is why every day the Foreign Secretary, Defence Secretary and I are speaking to our Nato allies.
And it is why I will speak to President Putin next week and they will both travel to Moscow in the coming days.
Russia should be under no illusion — a further invasion of Ukraine would be a historic mistake that would be a disaster for the world and, above all, a disaster for Russia.