The U.S. Treasury Department kept Japan on its monitoring list over currency practices in a report released on Thursday, warning against unnecessary foreign exchange market interventions.

In the semiannual report, the department said that Japan, which has a significant trade surplus with the United States and a current account surplus, should carry out interventions "only for very exceptional circumstances with appropriate prior consultations."

The Japanese government and the Bank of Japan conducted yen-buying, yen-selling interventions in April to May and in July, following the rapid depreciation of the yen. The report said that Tokyo is "transparent" with respect to its foreign exchange operations, noting that it discloses its intervention results every month.

China, South Korea, Singapore, Taiwan, Vietnam and Germany were also on the monitoring list. No trading partner was designated as a currency manipulator subject to strict sanctions.

The Treasury Department said China lacks transparency in its currency market interventions, and that the Chinese economy is "increasingly reliant on manufacturing investment amid a continued contraction in real estate investment."

It expressed worry about China's overcapacity stemming from state-led investments negatively impacting trade partners including the United States through the export of inexpensive goods.

The report, submitted to Congress twice a year, assesses countries and regions based on three criteria — a significant bilateral trade surplus with the United States, a large current account surplus, and unilateral and continuous foreign exchange market interventions. A trading partner is placed on the monitoring list if it meets two of the three conditions.

Japan had been off the monitoring list in the reports for June and November last year, but was put back on the list this June.