The Prime Minister also slammed Putin’s “barbarism” following a missile strike on a shopping mall in Ukraine that is said to have had more than 1,000 people inside. At least 10 people have died in that attack, although the number is likely to rise as rescuers remove the rubble.
Mr Johnson warned that the “price of freedom was worth paying” and said the G7 nations would continue to support Ukraine.
Speaking to the BBC, the Prime Minister said: “I think that sometimes the price of freedom is worth paying. Just remember, it took the democracies in the middle of the last century a long time to recognise that they had to resist tyranny and aggression.
“It took them a long time, it was very expensive, but what it bought in the end with the defeat of the dictators – particularly of Nazi Germany – it brought decades and decades of stability, a world order that relied on a rules based international system.
“That is worth protecting, that is worth defending.”
Following the attack on the crowded shopping mall-turned-shelter, Mr Johnson slammed Putin’s “barbarism and cruelty”.
He said: “This appalling attack has shown once again the depths of cruelty and barbarism to which the Russian leader will sink.
“Once again our thoughts are with the families of innocent victims in Ukraine.
“Putin must realise that his behaviour will do nothing but strengthen the resolve of the Ukraine and every other G7 country to stand by the Ukraine for as long as it takes.”
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The G7 is an informal meeting of some of the world’s developed democracies. The group used to be known as the G8 until Russia’s membership was suspended in 2014 following its annexation of Crimea in Ukraine.
Ukrainian President Volodymyr Zelensky addressed the leaders of the G7 countries virtually. He asked for more advanced air defence systems, a request made poignant by the missiles striking Kyiv and other Ukrainian cities over the weekend.
He also claimed that the sanctions against Russia were “not enough” and urged the leaders to help Ukraine unblock its ports and export much-needed grain to the world.
He said: “This confirms that sanctions packages against Russia are not enough, that Ukraine needs more armed assistance, and that air defence systems – the modern systems that our partners have – should be not in training areas or storage facilities, but in Ukraine, where they are now needed.”
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There has been concern that some European powers may be losing the resolve to continue supporting Ukraine as domestic issues including inflation and skyrocketing energy prices hit home.
This could see some nations push for a negotiated settlement with Russia, something which Ukraine has ruled out.
So far, however, support for Ukraine has remained strong, particularly from the UK and the US. Ukrainian President Zelensky has previously praised the UK for its fast delivery of advanced weapons, and Prime Minister Boris Johnson has been one of the most outspoken in his support for Ukraine.
In a video statement, Mr Zelensky said: “Words turn into actions. That’s the difference between Ukraine’s relationship with Great Britain and other countries. Weapons, finance, sanctions – on these three issues, Britain shows leadership.”