US President Donald Trump says he will immediately restore tariffs on US steel and aluminum imports from Brazil and Argentina.

"Brazil and Argentina have been presiding over a massive devaluation of their currencies, which is not good for our farmers. Therefore, effective immediately, I will restore the Tariffs on all Steel & Aluminum that is shipped into the US from those countries," Trump said in a tweet.

Trump also urged the Federal Reserve to prevent countries from gaining an economic advantage by devaluing their currencies.

"The Federal Reserve should likewise act so that countries, of which there are many, no longer take advantage of our strong dollar," Trump tweeted.

"Lower Rates & Loosen - Fed!", he said.

Trump has repeatedly urged the Fed to lower rates to below zero, arguing that negative rates in Europe and elsewhere give those countries and blocs a competitive advantage.

However, Fed policymakers have been reluctant to take the unorthodox policy steps tried by other global central banks. 

The US central bank's policy making committee holds its next meeting on December 10th and 11th.

Brazilian president Jair Bolsonaro said he would appeal to Mr Trump to show understanding towards Brazil in a looming row over fresh steel and aluminum tariffs.

"I hope that he understands and does not penalise us," Mr Bolsonaro said in a radio interview.

Argentina's Foreign Ministry said it would begin negotiations with the US State Department following the tariff restoration.