The declaration also came days after Trump - in a turnabout from his campaign stance - declared in an interview that his administration would not label China a currency manipulator, which could have triggered investigations.
China, Germany, Japan, Korea, Switzerland and Taiwan remained on a previously established watch list of countries in the Trump administration's first report on currency values.
According to the central bank, Taiwan only met one of the three criteria in the latest report as Taipei still enjoyed a large current account surplus, but did not meet the criterion which accused a trading partner of persistent one-sided currency intervention.
The report uses three criteria - a significant bilateral trade surplus with the USA; a material current-account surplus; and involvement in persistent one-sided intervention in the foreign-exchange market - to determine whether a trading partner is to be named a currency manipulator. The Treasury acknowledged that China has been intervening in currency markets to prevent a depreciation of the yuan, though it said its selling of foreign currency reserves abated in the early part of this year.
"Treasury estimates that during 2016 Korea was a net seller of foreign exchange of about $6.6 billion (0.5 percent of GDP)".
Despite Trump's argument that China is taking North Korea seriously, China remains adamantly opposed to US deployment of an advanced missile defense system in South Korea.
Snyder conceded that there is a greater risk under the Trump administration of U.S. unilateral action but said that the more Trump learns about this issue, the more he will understand the constraints faced by the United States.
Last Friday, US officials were reported to have said that President Trump's advisers discussed a range of ideas to get North Korea to abandon its nuclear programme.
Since Trump and Xi met, China has reduced coal shipments and threatened the oil trade with North Korea.
Although Beijing has allowed the yuan to slowly appreciate in recent years and actively fought depreciation recently, its past interventions "imposed significant and long-lasting hardship on American workers and companies".
Speaking with the Journal, Trump said he changed his mind because China hadn't been manipulating its currency for months, and that such a move could harm ongoing talks with Beijing on containing the nuclear threat from North Korea. China was labeled a currency manipulator between 1992 and 1994. If the same goods - iPhones, say - that were previously produced in China or Mexico were produced in the USA instead, they would very likely be more expensive, and perhaps many fewer would be produced and sold.
'They're not currency manipulators, ' said Trump, adding that China has not been manipulating its currency for months.
Trump did say he thought the dollar was "getting too strong" - a comment that sent the USA currency falling, though it subsequently rebounded.
A senior Asian diplomat who asked not to be named said the North Koreans are "coldly rational", and noted that the show of force by the United States "is as much directed towards China as North Korea".