Prime Minister Boris Johnson made a statement at the NATO press conference.
When NATO was founded more than 75 years ago, its members made a commitment to collective security that was unlike anything in previous history.
And when the Berlin Wall fell the people of Europe made it clear they wanted a future where their freedom and their security are inextricably tied together.
That is why NATO agreed that any country should be free to pursue the security alliances that it, that country chose.
And we must resist, we must oppose any return to the days when the fates of nations are decided over their heads by a handful of great powers.
And I want to stress this is not just about Russia, just as NATO itself is not just about Russia, of course not.
This is about upholding the founding principles of an alliance which, perhaps more than any other institution, has brought stability and peace, prosperity to the world.
And that must be the bedrock of our diplomatic efforts.
The UK's commitment to European security is unconditional and immovable. We have the biggest defence budget in Europe and the second largest in NATO.
We have contributed more troops than any other ally to NATO's enhanced Forward Presence.
And today I have agreed with the Secretary General a package of support to strengthen further our collective security, sending troops, planes and ships to defend NATO from north to south.
Earlier this week I met the Prime Minister of Lithuania and I will be travelling shortly to Poland.
And these are the countries where every day the population wakes up with an acute awareness of the threat just across their border.
And they are countries whose voices and views must be at the heart of every discussion we have.
Because I believe that if we can keep a strong grip on the fundamentals, those fundamental principles that define our alliance and combine strong deterrence with patient diplomacy, then we can find our way through this crisis.
But the stakes are very high and this is a very dangerous moment.
And at stake are the rules that protect every nation, every nation - big and small.
Thank you all very much.