The Japanese yen is heading for its worst monthly drop since July, after the Bank of Japan opted to keep rates unchanged at 0.5% and offered a less hawkish future-rate tone than markets anticipated. At the same time the U.S. dollar climbed toward a three-month high, propelled by comments from the Federal Reserve signaling fewer imminent rate cuts. Weak export-order data from Japan added downward pressure on the yen. The currency dynamics are raising concerns about emerging-market currency risk and export competitiveness in Asia.