The UK backs Ukrainian troops carrying out strikes in Russian territory, the armed forces minister has said, calling it “not necessarily a problem” if Ukraine uses weapons donated by Britain. James Heappey said the UK believed it was “completely legitimate” for Ukraine to identify targets in Russia in order to disrupt attacks on Ukraine. Responding to the comments, Moscow warned Britain that if it continued to help Ukraine to strike targets in Russia then there would be an immediate “proportional response”. Heappey told Times Radio: “Ukraine was a sovereign country that was living peacefully within its owner borders and then another country decided to violate those borders and bring 130,000 troops across into their country. “That started a war between Ukraine and Russia, and in war Ukraine needs to strike into its opponent’s depth to attack its logistics lines, its fuel supplies, its ammunition depots, and that’s part of it.” He added that it was “completely legitimate for Ukraine to be targeting in Russia’s depth in order to disrupt the logistics that if they weren’t disrupted would directly contribute to death and carnage on Ukrainian soil”. He said it was “not necessarily a problem” if British-donated weapons were used to hit sites on Russian soil after accepting that weapons allies were supplying to Ukraine had the range to be used over borders. “There are lots of countries around the world that operate kit that they have imported from other countries. When those bits of kit are used we tend not to blame [the country] that manufactured it, you blame the country that fired it.” Heappey said there was “every chance” the Ukrainians would be able to repel the Russian forces, a more optimistic tone than struck by Boris Johnson in India last week. The prime minister said that a war of attrition in Ukraine meant Russia could grind out an eventual victory and “the sad thing is that that is a realistic possibility”. Heappey said that in the east of the country the conflict would be between two forces that were “much more evenly balanced, where the Ukrainians have the advantage of defensive positions that have been dug in and prepared over the last eight years and that’s going to make it an extraordinarily difficult nut for the Russians to crack”. “And with all the support that the Ukrainians are getting from around the world, there’s every chance the Ukrainians can see them off,” he told Sky. Speaking earlier on the BBC, Heappey said the Russian president, Vladimir Putin, was determined to claim some kind of victory before the 9 May victory parade, a time pressure he said would force errors by the Russians. He said commanders would know it was “militarily unsound” to attempt to keep to a set date. “It is absolute folly to launch an offensive before you’ve massed all of your combat power and that they’re giving away whatever advantage they may have won and there’s been incredibly bad weather in the Donbas over the last week or two, which means the ground is not conducive right now to the manoeuvre of heavy army,” Heappey said. “Putin’s political pressure and the hubris that he’s shown, his desire to stand there on the steps of the Kremlin on 9 May and be a hero, means that thousands of Russian lives are going to be lost and the Russians are going to hand over the numerical advantage that they should have.”