It came after Ukrainian president Volodymyr Zelenskyy appealed to other nations, saying: “Who is ready to fight with us? Honestly, I don’t see anyone . . . I’m asking them, are you with us?”.

He also warned that Putin was trying to assissinate him and his family. 

Ben Wallace

Speaking on the Today programme, Mr Wallace explained the decision not to deploy was “not about risk”.

He said: “It’s not about risk, as much as I care for my personnel. It’s not about risk, it’s about if we were to directly attack Russian aircraft, we would have a war across Europe.”

He added: “I have said continually for a long time, as has Britain, and the Prime Minister has supported this position, that Putin is not rational.

“He is trying to invade Ukraine. He won’t stop.

“He will use everything in the Baltic states. He doesn’t believe the Baltic states are really countries.

“And we will have to stand up to it.

“Now, I cannot trigger a European war and I won’t trigger a European war. But what I will do is help Ukraine fight every street with every piece of equipment we can get to them, and we will support them, and that is the reality.”

Asked about a no-fly zone, Mr Wallace said to implement one he would “have to put British fighter jets directly against Russian fighter jets.”

He added: “Nato would have to effectively declare war on Russia because that’s what you would do.”

The Defence secretary stressed that weapons were being sent to Ukraine to help its army with the conflict, from the US and UK, explaining: “A number of the Baltic states, the United States provided Stinger missiles, which has brought down clearly a number of Russian aircraft.

“The ability to defend their airspace from [the] ground has been enabled. And [of] course, there is more to do and… we’ve been asked and a number of other nations [have been asked] for that.”

Early this morning, Boris Johnson spoke with Mr Zelenskyy, who updated the Prime Minister on the continuing and advancing conflict.

Following the call, a Downing Street spokesman said: “President Zelenskyy updated the Prime Minister on the most recent Russian military advances, including missile and artillery strikes on Ukrainian cities and the terrible developments in Kyiv in the early hours of this morning.

“The Prime Minister assured President Zelenskyy that the world is united in its horror at what Putin his doing. He paid tribute to the bravery and heroism of the Ukrainian people in standing up to Russia’s campaign of violence, and expressed his deep condolences for those who have been killed.

“The Prime Minister committed to provide further UK support to Ukraine in the coming days as the people of Ukraine and the world continue to demonstrate that Putin cannot act with impunity.”

Western officials said that Russia’s aim of surrounding Kyiv and taking the city of Kharkiv had been slowed by Ukrainian resistance, which was stronger than expected.

Mr Zelensky delivered an early morning address to his country as his army warned Russian troops were “moving at speed” towards central Kyiv followed by a column of military trucks. He also warned that there was a plot to have him assassinated, saying that “enemy saboteur groups” were already in Kyiv and that Russia was planning to kill him.

He said: “The enemy has identified me as the number-one target.

“My family is the number-two target. They want to destroy Ukraine politically by destroying the head of state.”

Meanwhile Putin spoke with Emmanuel Macron, the French president, last night – his first call with a Western leader since he declared two independent states in Ukraine and launched his attack.

The leaders had a “serious and frank exchange of views about the Ukraine situation”, the Kremlin said.

A French official said Macron called Putin just before an EU summit in Brussels to demand “the immediate halt of Russian military operations”.

Last night Putin announced retaliatory moves against the UK, after Mr Johnson yesterday set out the toughest sanctions package ever imposed on a country.

Russia’s civil aviation authority has banned UK flights to and over Russia, after the UK banned Aeroflot from landing in the UK.

Rosaviatsiya said that all flights by UK carriers to Russia as well as transit flights have been banned, starting today

It said the measure was taken in response to the “unfriendly decisions” by the British authorities who banned flights to the UK by Russian flag carrier Aeroflot as part of sanctions over Russia’s invasion of Ukraine.