Boris Johnson said it was “deeply heartbreaking” and “absolutely distressing” to deny President Volodymyr Zelenskyy a no-fly zone over Ukraine.
The Prime Minister, speaking to Sky News’ Beth Rigby interview programme, said the pair had had ‘very frank conversations’ but the UK and NATO could not cross that line .
On Wednesday, Mr Zelenskyy told Sky News special correspondent Alex Crawford in Kyiv that Western countries were undecided on the issue of “closing the heavens” against what he called “the Nazis”.
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“If you are united against the Nazis and this terror, you must shut down. Don’t wait for me to ask you many times, a million times. Shut down the sky,” he said.
“Close the skies and stop the bombings.”
He also made the call during a historic live video address to MPs in the House of Commons on Tuesday.
But the UK, US and NATO have continually rejected Mr Zelenskyy’s calls for a no-fly zone over Ukraine because they say it would mean having to shoot down Russian planes, which would probably start another world war.
Mr Johnson and the Ukrainian leader had almost daily conversations in the 15 days following Russia’s invasion.
The Prime Minister said: “We’ve had some very frank conversations and others that have been deeply upsetting because there is a line beyond which, quite frankly, the UK and NATO would be considered to be in direct conflict with Russia.
“It’s scary, absolutely scary. I’ve had this conversation at least twice with Volodymyr, but I think the difficulty is that I’ll have to command RAF jets, British pilots in the air with a mission to quickly shoot down Russian jets.”
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Mr Johnson also told the program he fears that Vladimir Putin will deploy chemical weapons in Ukrainereiterating the fears of Western officials after Moscow accused Kiev of planning to deploy them to the battlefield.
“The things you hear about chemical weapons are straight out of their playbook,” he said.
“They are starting to say that there are chemical weapons that have been stockpiled by their adversaries or by the Americans.
“And so when they deploy chemical weapons themselves, as I fear, they have some kind of maskirovka – a fake story – ready to go.
“You’ve seen it in Syria. You’ve seen it even in the UK. They’re already doing that. It’s a cynical, barbaric government.”
Russia “has the capacity and the capacity”
On Wednesday, Moscow said it had uncovered a military bioweapons program in Ukraine involving deadly pathogens such as plague and anthrax and called on the United States to explain the “Ukrainian bioweapons lab.”
A US official dismissed the claim as “absurd propaganda” and accused Russia of seeking retroactive pretexts for war. Analysts said Russia’s claims could be the seeds of what could turn out to be a “false flag” move.
And White House press secretary Jen Psaki has since been asked about the chances of Russia using chemical weapons. She said, “They have the capacity and the ability.”
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Asked about Mr Johnson’s warning, former British intelligence officer Christopher Steele told Sky News: ‘I certainly think if you look at what happened in Syria and Chechnya and of course what happened on our own streets in Salisbury, I wouldn’t rule it out at all.
“I think as the Russian military gets bogged down and obviously doesn’t achieve its military objectives, you’re likely to see more killing and indiscriminate bombing and possibly the use of chemical weapons.”
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