In an early tweet, the president announced he is restoring tariffs on aluminum and steel shipped from Argentina and Brazil, reports the Wall Street Journal. Brazil and Argentina later secured "permanent exemptions" from the levies.
In March 2018, Trump authorized a 25 per cent tariff on steel imports and a 10 per cent duty on aluminum - import barriers that heralded the start of his administration's hawkish push on trade - after a government report found that foreign shipments of the metals imperil national-security interests.
Last year, after having accused the two South American countries of weakening their currencies to get an unfair advantage, the USA president imposed a 25 percent tariff on steel and a 10 percent duty on aluminum.
Brazil's President Jair Bolsonaro said he would seek talks with Mr Trump. However, he also expressed hope that Trump would show mercy to Brazil's commodity-based economy.
In a tweet posted just after 6 a.m., Trump said the countries have been "presiding over a massive devaluation of their currencies" which he says is bad for American farmers. Our economy basically comes from commodities, it's what we've got.
Argentine Production Minister Dante Sica said Trump's announcement was "unexpected" and he was seeking talks with USA officials.
The president also said that the Federal Reserve should lower rates in order to devalue the USA dollar, which would make US products more competitive on the global market place.
Trump accused both countries of manipulating their currencies to hurt United States farmers, and he paired his action with criticism of the Federal Reserve, notes Bloomberg, which sees the morning moves as significant.
Trump has repeatedly urged the Fed to lower rates to below zero, saying negative rates in Europe and elsewhere give those countries a competitive edge.
However, Fed policymakers have been reluctant to take the unorthodox policy steps tried by other global central banks.