The move, which comes as Ukrainian troops in Russia’s Kursk region brace for an assault by tens of thousands of Russian and North Korean troops, represents an about face for the White House which has long refused to allow Kyiv to use Army Tactical Missile Systems deep inside Russia.

Washington’s decision to let Ukraine strike deep into Russia with long-range U.S. missiles could lead to World War Three and will receive a swift response, Vladimir Dzhabarov, first deputy head of the Russian upper house’s international affairs committee, said on Sunday, according to the TASS news agency.