на фоне усиливающихся опасений(по поводу – over: Prime Minister Justin Trudeau announced last week $62.5 million is being provided for Canada's fish and seafood sector amid mounting concerns over the state of the country's food supplyTamerlane)
при неблагоприятных погодных условиях(при заходе на посадку при неблагоприятных погодных условиях вертолет столкнулся с поверхностью моря и затонул на глубине 6 м)
на фоне слухов(Shares in the bookseller's owner, HMV, climbed 12.5% amid speculation that billionaire Alexander Mamut had put in a new offer in an attempt to clinch control of the 314 Waterstone's outlets in Britain and Ireland. TG Alexander Demidov)
