At Tuesday's press conference in Poland, Boris Johnson was confronted by a tearful Ukrainian woman who had fled her country amid Vladimir Putin's invasion.
Daria Kaleniuk, a Ukrainian journalist, gave an impassioned plea for a 'no-fly zone' over Ukraine, which has been hit by a fierce airstrike from Russian troops since last week.
She told the prime minister, who appeared in Warsaw alongside the Polish prime minister Mateusz Morawieck, that it is "Ukrainian children who are there taking the hit".
Mr Johnson rejected her calls, insisting that disastrous consequences would follow if UK forces engaged in combat with Russians.
Ms Kaleniuk, who said she is from Kyiv but entered Poland a couple of days ago, said allies from the Nato defence alliance are wrong to rule out the step out of a fear of provoking a nuclear war.
But what would a 'no-fly zone' mean for Ukraine - and why is the UK government against imposing one?
What is a 'no-fly zone' and what would it mean for Ukraine?
Imposing a no-fly zone over Ukraine would prevent Russia's military aircraft from entering the country's air space.
If Russian aircraft did enter Ukrainian airspace, they would be breaching the no-fly zone and would be at risk of being shot down.
Ms Kaleniuk put forward an emotional plea for the measure.
She told today's press conference: “Ukrainian women and Ukrainian children are in deep fear because of bombs and missiles which are going from the sky. Ukrainian people are desperately asking for the rights to protect our sky, we are asking for a no-fly zone."
She said Mr Putin’s children are safe in mansions that have not been seized and, breaking into tears, added: “I don’t see that. I see that my family members, that my team members are saying we are dying, we don’t have anywhere to run.”
Ukraine's president Vlodymir Zelenskly reportedly asked US president Joe Biden for a no-fly zone earlier this week, while Ukraine’s ambassador to the UK had previously called on Nato to impose one.
In a briefing with journalists in London, Vadym Prystaiko, said Ukraine needed “something which only Nato can provide” to help the state defend itself against Russian forces.
How has the UK and Nato responded?
Mr Johnson said he welcomed Ms Kaleniuk's passionate question and was “glad” she had made it to Poland, saying he was “acutely conscious that there is not enough we can do as the UK government to help in the way that you want”.
Mr Johnson said that “unfortunately the implication of that is the UK would be engaged in shooting down Russian planes, would be engaged in direct combat with Russia – that’s not something we can do”.
“I think the consequences of that would be truly very, very difficult to control,” he added.
Instead, Mr Johnson argued Britain must continue with “tightening the economic noose” around the Putin regime and providing further defensive support to Kyiv.
Mr Johnson clarified that the UK is not actively supporting British nationals volunteering to help the defence of Ukraine, contradicting an earlier remark from Foreign Secretary Liz Truss.
“I think for any Nato member to get involved actively in conflict with Russia is a huge step which is not being contemplated by any member,” Mr Johnson stressed during a press conference against the backdrop of armoured vehicles, at the Tapa military base in Estonia.
“It’s very very important to understand Nato is a defensive alliance.
“This is a time when miscalculation and misunderstanding is all too possible and it’s therefore crucial that we get that message over.
“When it comes to a no-fly zone in the skies above Ukraine we have to accept the reality that that involves shooting down Russian planes … that’s a very, very big step, it’s simply not on the agenda of any Nato country.”
In a round of broadcast interviews, Deputy Prime Minister Dominic Raab echoed the message.
He said: “Putting UK forces in the position where they would be directly required to shoot down Russian planes, I agree with the analysis… both in terms with feeding (Vladimir) Putin’s narrative, but also from the point of the view of the distinction between what we would do for a Nato ally and the Ukraine, which is a close partner, we want to support, but we will not get involved directly in military operations against Russian forces.
“We have considered a no-fly zone but, for the reasons I’ve given, the international community as a whole has decided against it.”
Defence secretary Ben Wallace has rejected the calls on a number of occasions
He warned that shooting down a Russian plane could trigger a Europe-wide conflict between Mr Putin and Nato.
A no-fly zone would also have to apply to Ukrainian jets, meaning they could not target Russian forces from the air, he added.
“If you had a no-fly zone in Ukraine, the overwhelming scale of the Russian army would be able to drive around with impunity, which it can’t at the moment.”
But he said the UK had “led the way” in supplying surface-to-air weapons systems to Ukraine.
“There are two ways to achieve a no-fly zone. One is the way that Britain has led the way in, which is arming the Ukrainians with anti-air capabilities, from the ground to the air, and the reason they are doing the bombing at night is because they can’t – because of those weapon systems – the Russians cannot fly much in the day."
However, some MPs have been reluctant to rule out the measure completely.
Former Cabinet minister David Davis has called for Nato allies to provide air support to the Ukrainian army to assist the fight against Russian invaders.
“It is far too late to get boots on the ground but it is not too late to provide air support to the Ukrainian army which may neutralise Putin’s overwhelming armoured superiority,” he tweeted.
“If this is confined to the airspace over Ukraine, and is based on a request from President Zelensky, this should be perfectly legal under almost any interpretation of international law. It will also reduce the risk of escalation.”
Tobias Ellwood, Conservative chairman of the Defence Committee, said Nato should not rule out “the formation of a potential no-fly zone”.
The MP told ITV News: “We need to reconsider this no-fly zone, let’s say west of the Dnieper River, because that would change the optics here.”
Mr Ellwood added: “If we don’t stand our ground now, where will this go? And don’t forget there are other adversaries around the world, namely China, watching very carefully how the West reacts here.”
