On Wednesday, the US labeled Switzerland and Vietnam as currency manipulators and added India, Taiwan and Thailand to a watch list of countries it suspects of taking measures to devalue their currencies against the dollar.
Others already on the "monitoring list" are China, Japan, Korea, Germany, Italy, Singapore and Malaysia. The new additions take the list to 10.
The US Treasury also said that India and Singapore had also intervened in the foreign exchange market in a "sustained, asymmetric manner" but did not meet other requirements to warrant designation as manipulators.
While being designated as a currency manipulator comes with no immediate penalties, it can rattle financial markets.
The US government had removed India from the monitoring watch list in May 2019.
The US Treasury under the departing administration of President Donald Trump said that through June 2020 Switzerland and Vietnam had intervened heavily in currency markets to prevent effective balance of payments adjustments.
In response to this allegation, the US Swiss National Bank said it does not manipulate its currency and its monetary policy approach would be unchanged, adding that it "remains willing to intervene more strongly in the foreign exchange market".