But Ben Wallace dismissed the proposal outright – as he gave a bullish assessment of Russia’s advance being slowed, as it failed to achieve “any of its major objectives” on day one of the invasion.
“To do a no-fly zone, I would have to put British fighter jets directly against Russian fighter jets,” the defence secretary said.
“Nato will have to effectively declare war on Russia, because that’s what you would do.”
Lesia Vasylenko, a Ukrainian MP, told Mr Wallace: “We are at war. What we need now, and this is imperative to understand, we need the closure of the airspace above Ukraine.
“Throughout the night, hardly anyone from Kyiv slept because they were attacks, there were planes flying in.”
But the defence secretary, speaking on BBC Radio 4, insisted: “If we were to directly attack Russian aircraft, we would have a war across Europe.”
On Thursday evening, Boris Johnson had played down the prospects of a no-fly zone while appearing to leave the door ajar.
“I understand the attractions of the no-fly zone,” he told MPs, while warning the prospect of downing Russian planes was something MPs should “contemplate with caution.”
Pressed again, the prime minister said: “We are trying to keep all our options open”, though he said there had to be “a dose of realism about what we can do on the military front.”
Mr Wallace also blamed other, unnamed, Nato nations for Ukraine remaining outside the military bloc – when the UK had been pushing for its admission since 2008.
“Other nations didn’t want them to come in at the same pace. So the reality is, Ukraine isn’t in Nato,” he said.
Earlier, the defence secretary insisted Russia is failing to achieve any of its key aims at the start of its invasion and has lost 450 personnel.
“Our assessment, as of this morning, is that Russia has not taken any of its major objectives - in fact it is behind its hoped-for timetable,” he said.
And he added: “Russia has lost significant amounts of armour and people – Ukrainians are fighting and they are fighting brave.”
The assessment came despite an expectation that Russian tanks will roll into Kyiv on Friday – evoking memories of Soviet invasions of the capitals of Hungary and Czechoslovakia in the last century.
Russia has continued to carry out missile attacks, as Volodymyr Zelensky, the Ukrainian president, pleaded with Western allies to do more to stop Russia’s assault.
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