KYIV (Reuters) – British Prime Minister Boris Johnson warned on Tuesday that a Russian invasion of Ukraine would lead to a military and humanitarian disaster. Russia, which seized Crimea from Ukraine in 2014 and backs separatists in the east of the country, has amassed tens of thousands of Russian troops near Ukraine, leading to fears in the West that Moscow could invade. “A further Russian invasion of Ukraine would be a political disaster, a humanitarian disaster, and in my view it would also be for Russia and the world a military disaster,” Johnson said at a press conference on a visit to Ky…