Ford Motor Co. Chief Executive Officer Alan Mulally said he is concerned that the depreciation of the yen is bolstering the competitiveness of Japanese carmakers.

"The most important thing that most countries around the world believe in is letting the markets determine the currency," Mulally told a recent Bloomberg Television program from Bangkok in reference to the Japanese currency. "That's just so important to all of us in the international trading system."

The yen has fallen about 15 percent against the dollar since mid-November, when Shinzo Abe, then successfully angling to become prime minister, began a campaign to talk down the value of the currency to revive the nation's export-led economy. That has bolstered shares of Toyota Motor Corp., Nissan Motor Co. and Honda Motor Co.