Tensions have risen to their highest level between Russia and the United States since the 2014 Russian annexation of the Crimean peninsula, which is internationally recognised as part of Ukraine. Moscow has sent an estimated 100,000 troops to the Russia-Ukraine border, though it has denied planning to attack its western neighbour. The deployments, it said, serve as a warning to keep Ukraine out of Nato. Washington has said it is committed to helping Ukraine defend its “sovereign territory”, but…