No major U.S. trading partners are manipulating their currencies to gain an unfair trade advantage, the Treasury said Friday, although China is on its monitoring list.

"Most foreign exchange intervention by U.S. trading partners last year was in the form of selling dollars, actions that served to strengthen their currencies. However, Treasury remains vigilant to countries’ currency practices and policy settings and their consistency with strong sustainable and balanced global growth,” Secretary of the Treasury Janet Yellen said in a statement.

"China’s failure to publish foreign exchange intervention and broader lack of transparency around key features of its exchange rate mechanism make China an outlier among major economies and warrant Treasury’s close monitoring," the report said.

In its semiannual report to Congress, Treasury also said it will continue to conduct an in-depth analysis of Switzerland and reiterated a call for increased transparency from China. The monitoring list also includes Korea, Germany, Malaysia, Singapore, Switzerland, and Taiwan.