TOKYO  - Japan will express concern if currency rates move rapidly in a way that deviates from economic fundamentals, the country's top currency diplomat said on Friday.

Masatsugu Asakawa, vice finance minister for international affairs, said bond and currency markets have been reacting to heightening market expectations that the U.S. Federal Reserve will cut interest rates as early as next month.

"If the Fed does cut rates in July because it feels doing so would be necessary to prevent a U.S. economic downturn, that's an appropriate monetary policy decision," Asakawa told a news conference.

"But if exchange rates are moving rapidly in a way that cannot be explained by economic fundamentals, Japan has no choice but to voice concern," he said.

(Reporting by Leika Kihara; Editing by Chris Gallagher) ((leika.kihara@thomsonreuters.com; +813-6441-1828; Reuters Messaging: leika.kihara.reuters.com@reuters.net))