The prime minister and the Ukrainian president have been having almost daily phone calls in which Boris Johnson has had to say he cannot support a NATO no-fly zone.
Boris Johnson says it has been “deeply upsetting” and “absolutely agonising” to refuse President Volodymyr Zelenskyy a no-fly zone over Ukraine.
The prime minister, speaking to Sky News’ Beth Rigby Interviews programme, said the pair have had some “very frank conversations” but the UK and NATO cannot cross that line.
On Wednesday, Mr Zelenskyy told Sky News’ special correspondent Alex Crawford, in Kyiv, that Western countries were being indecisive on the issue of “closing the skies” against what he called “the Nazis”.
The Ukrainian president had said: “If you are united against the Nazis and this terror, you have to close. Don’t wait for me ask you several times, a million times. Close the sky.
“Close the sky and stop the bombing.”
He also made the plea during a historic live video address to MPs in the House of Commons on Tuesday.
But the UK, the US and NATO have continually rejected Mr Zelenskyy’s calls for a no-fly zone over Ukraine as they say it would mean having to shoot down Russian planes, which would likely start another world war.
Mr Johnson and the Ukrainian leader have been having almost daily conversations in the 15 days since Russia invaded.