UK Foreign Secretary Liz Truss holds frosty news conference with Russian counterpart
Sergei Lavrov says relations between UK and Russia leave "much to be desired"
Meanwhile Truss accuses Russia of "Cold War rhetoric"
In Brussels, Boris Johnson warns the Ukraine-Russia crisis is at its "most dangerous moment"
The UK PM then went to Poland as part of a diplomatic push
Russia has been massing troops on its neighbour's borders and in Belarus for months
And Johnson warns the intelligence on a possible invasion "remains grim"
Boris Johnson has arrived for his flight from Brussels to Warsaw following his meeting and press briefing with the Nato secretary general.
The UK prime minister and Jens Stoltenberg held talks for about 35 minutes about Nato's response to Russia amassing troops on the Ukrainian border, before taking media questions.
Johnson is due to hold talks later with the Polish Prime Minister, Mateusz Morawiecki.
This is about upholding Nato founding principles - PM
Meanwhile, the UK Foreign Secretary Liz Truss says Lavrov has told her that Russia has "no plans" to invade Ukraine.
But she says "we need to see those words followed up by actions", adding: "We need to see the troops and the equipment that is stationed on the Ukrainian border moved elsewhere.
"At present, it is in a very threatening posture," she adds.
And now let's go back to the Truss-Lavrov news conference in Moscow.
Russia's foreign affairs chief says Russia is not "trying to coerce or threaten anyone".
He says it is Russia that is being threatened - including by Truss in the House of Commons.
He claims there has been no Russian aggression over Ukraine.
James Landale
Diplomatic correspondent
What came across at Prime Minister Boris Johnson’s news conference at Nato was the sense of urgency.
Both he and Nato chief Jens Stoltenberg said these coming days were “a very dangerous moment” for European security.
Specifically, Johnson said this was “the most dangerous moment in what is the biggest security crisis that Europe has faced in decades”.
This is a message that is echoed by officials and diplomats in private briefings.
There is a sense that this confrontation may be coming to a head, hence the increased flow of politicians heading to Moscow, with offers of diplomacy - but also warnings of deterrence.
James Landale
Diplomatic correspondent
This is significant. Boris Johnson has just suggested the UK might be willing to support a military insurgency in Ukraine with arms if Russia were to invade.
He said Britain had already given Ukraine 2,000 anti-tank weapons and, at the moment, Ukraine was not asking for more.
But when asked if the UK could give more, he said: "It is possible, I don’t want to rule it out."
He added: “We will consider what more we could conceivably offer.”
This reflects a similar debate taking place in Washington about whether more military elements could be included in the West’s largely economic package of deterrence.
And - finally - back to Brussels and Boris Johnson.
In response to a question from BBC political editor Laura Kuenssberg, he says the Ukrainian army is now "very large", estimating it as 200,000 strong.
"It's my judgement, I think it is certainly the judgement of Nato, that they will fight," he says.
"I just want to stress that it would be an absolute disaster if it were to come to that and if there were to be serious bloodshed on Ukrainian soil."
Johnson says that people in Russia must be thinking about this and "whether it is really sensible to spend the blood of Russian soldiers in a war which I think would be catastrophic".
He concludes by saying there is a very good opportunity to talk - and with that, the news conference in Brussels has come to a close.
But Sergei Lavrov plays down suggestions that his country is planning to invade Ukraine - saying that the US and Ukraine itself did not believe Russia would invade.
“Unfortunately our attempts to explain ourselves have fallen on deaf ears,” he says.
“Either our counterparts are not aware of the facts or are deliberately ignoring them.”
And now we're going back to Moscow. Foreign Secretary Liz Truss, at a joint press conference with Russian counterpart Sergei Lavrov, says the "future peace and stability" of Europe is at stake.
"There is still time for Russia to end its aggression towards Ukraine and pursue the path of diplomacy.
"But Nato is very clear that if that path is not chosen there will be severe consequences for Russia, Ukraine and the whole of Europe."
Alongside the UK PM, Stoltenberg warns that Russia has a "clear choice" - they can either choose the diplomatic solution, or if they choose confrontation "they will pay a high price".
He says this will consist of economic sanctions, as well as an increased Nato military presence in the eastern part of the alliance - with UK a key part of this.
This, he explains, is in addition to the Ukrainian defence force - which he says is much stronger now than in 2014, bolstered by better equipment and command.
Back in Brussels, Boris Johnson goes on to say that the UK is preparing militarily and economically, but is also willing to talk.
"There are some things which are non-negotiable... that Nato must have an open-door policy," he says, referring to not ruling out Ukraine ever joining the defence pact.
But he adds there are things which can be discussed.
The prime minister ends on the question of whether Nato's efforts are going to pay off. "I simply can't say," he says.
It's now UK Foreign Secretary Liz Truss's turn.
She says the aggression by the Russian government towards Ukraine is “seriously undermining” Russia’s standing in the world.
She warns of a “prolonged and drawn out conflict” but says there is an “alternative path” Russia can take.
“Russia has a choice which can result in a better future for Europe, Russia and the Russian people."
And here's more from Sergei Lavrov, the Russian foreign affairs chief.
Relations between the UK and Russia “leave much to be desired” and are at the “lowest point over the past few years”, he says.
He adds: “This is not our fault."
It's a busy morning of diplomacy - while Boris Johnson is in Brussels with Nato's Jens Stoltenberg, UK Foreign Secretary Liz Truss is in Moscow giving a news conference with Russian counterpart Sergei Lavrov.
Lavrov tells reporters the movement of Russian troops has “stirred a lot of hysteria in the West”.
He says Russia wants a specific response to its security concerns, “not just words”.
"Today’s talks helped our British counterparts to understand how important all of these matters are to Russia,” Lavrov says.
Boris Johnson says Nato members made a commitment to collective security unlike anything in previous history.
He says when the Berlin Wall fell, the people of Europe made clear they wanted their freedom and security to be inextricably tied together.
The UK PM adds: "We must oppose any return to the days when the fates of nations are decided over their heads by a handful of great powers."
Answering journalists' questions, Boris Johnson says "our intelligence I am afraid to say remains grim".
He says "this is probably the most dangerous moment" in the biggest security crisis Europe has faced in decades.
He says that he does not think a decision on invading has been taken in Moscow - but says that doesn't mean something disastrous will not happen.
Johnson says that he thinks Europe is agreed over sanctions against Russia and says the tougher those are the more chance there is of deterring "what I think would be an irrational response".
Stoltenberg reveals that, this morning, he wrote to Russian Foreign Minister Sergei Lavrov, reiterating his wish to "continue our dialogue...to find a diplomatic way forward".
He says Nato is ready to listen to Russia's concerns - and discuss ways to hold and strengthen fundamental principles of European security.
Nato Secretary General Jens Stoltenberg begins by welcoming the UK's offer of troops, ships and planes - and says that it is a dangerous moment for European security.
He says the number of Russian forces is going up while the warning time for an attack "is going down".
He says that Nato must be prepared - while aiming for a diplomatic solution.
UK Prime Minister Boris Johnson and Nato Secretary General Jens Stoltenberg are giving a news conference now...
Image source, EPAWhile we wait for the start of their news conference, we've received these pictures of Foreign Secretary Liz Truss meeting her Russian counterpart, Sergei Lavrov.
They are holding talks in Moscow to discuss the Ukraine crisis. Their joint news conference has been delayed - we will keep you updated.
Image source, EPA