A US trade probe suddenly ordered by President Donald Trump on Brazil sent shockwaves through President Luiz Inacio da Silva’s government, according to a senior Brazilian diplomat who described it as an unwarranted threat that has helped to plunge relations to their lowest point in over a century.

U.S. Trade Representative Jamieson Greer said on Tuesday he had launched an investigation into Brazil's "unfair" trading practices, a week after President Donald Trump threatened a 50% tariff on imports from Latin America's largest economy.