The Russian prime minister, Dmitry Medvedev, has threatened to retaliate for the grounding of a subsidiary of Aeroflot, the national airline, because of EU sanctions, with one newspaper reporting that European flights to Asia over Siberia could be banned. Such a move would enforce costly detours on airlines, including Lufthansa and IAG, owner of British Airways, as more fuel would be needed for extended routes. Low-cost carrier Dobrolyot, operated by Aeroflot, suspended all flights last week after its airline leasing agreement was cancelled under European Union sanctions because it flies to Crimea, a region Russia annexed from Ukraine in March....