The Treasury Department said Friday that Japan and China remain on a list of countries it monitors over potentially "unfair" currency practices, but refrained from labeling any major U.S. trading partner as a manipulator.

In a semiannual report to Congress on currency manipulation, the department also called China an "outlier" among major economies, citing its failure to publish foreign exchange intervention data and a broader lack of transparency around key features of its exchange-rate mechanism.

"The activities of state-owned banks in particular warrant Treasury's close monitoring," the report said.