Britain today backed Ukraine if it wants to attack targets on Russian soil.
Defence minister James Heappey said it is “entirely legitimate” for Kyiv’s forces to use western-supplied weapons to launch strikes over the border.
It comes after a large fire erupted in the early hours yesterday at an oil storage facility in the city of Bryansk, 100 miles into Russia over the Ukrainian border.
Foreign Minister Sergei Lavrov claimed the risk of a third world war was “considerable”, saying according to his ministry: “I would not want to elevate those risks artificially. Many would like that. The danger is serious, real. And we must not underestimate it.
"NATO, in essence, is engaged in a war with Russia through a proxy and is arming that proxy. War means war."
Mr Heappey told the BBC that claim was “nonsense and Lavrov knows it”, as weapons have been donated directly by western countries and not by NATO itself.
Yesterday Britain announced it will send Stormer armoured vehicles equipped with anti-aircraft rocket launchers to Ukraine .
To date the UK has provided more than 5,000 anti tank missiles, five air defence systems with more than 100 missiles, 1,360 anti-structural munitions, and 4.5 tonnes of plastic explosives.
Britain has also sent over 90,000 ration packs, 10 pallets of medical equipment, 3,000 pieces of body armour, 77,000 helmets and 3,000 pairs of boots.
Asked if the UK would support Ukraine striking targets on Russian soil, Mr Heappey told BBC Radio 4’s Today programme: “The question is, is it acceptable for our weapons systems to be used against legitimate Russian military targets by the Ukrainians…
“It is entirely legitimate to go after military targets in the depth of your opponents to disrupt their logistics and supply lines.
“Just as, to be frank, providing the Russians don’t target civilians which unfortunately they’ve not taken too much regard for thus far, it’s perfectly legitimate for them to be striking targets in Western Ukraine to disrupt Ukrainian supply lines.
“That is very much a part of war and the Russians and Ukrainians are quite legitimate in going after those targets.”
He also told Times Radio “of course” Britain supports Ukraine hitting targets on Russian soil.
He said: “The fact is that 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 opponents depth to attack its logistics lines, its fuel supplies, its ammunition depots, and that's part of it."
He added that it is "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 is "not necessarily a problem" if British-donated weapons are used to hit sites on Russian soil after accepting that weapons now being supplied by allies to Ukraine have 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."
