The United States opted not to call China or other trading partners a currency manipulator.

The Treasury Department's semi-annual currency report, however, said a recent depreciation of the yuan will likely worsen the U.S. trade deficit with China.

The Chinese currency has fallen more than 9 percent against the greenback since the Treasury's last report on April 13.

Some China experts speculate Beijing could weaken its currency as a weapon in a trade war with the U.S. Treasury Secretary Steven Mnuchin criticized China's lack of currency transparency in the report.

But Bannockburn Global Forex chief market strategist Marc Chandler said, "To the extent that it (China) has intervened, it appears to be to slow even if not reverse the yuan's decline." In addition to China, the Treasury said it was also keeping a close eye on the currencies of India, Japan, Germany, South Korea and Switzerland.