Japan's foreign-exchange policy did not become a sticking point at Friday's U.S.-Japan summit, and an encouraged Bank of Japan might keep its aggressive monetary easing program in place as it tries to stoke 2 percent inflation.

But concerns are lingering that U.S. President Donald Trump, who is eager to reduce the trade deficit, may lambaste Japan again for manipulating the currency markets if the U.S. dollar extends gains against the yen.

The BOJ's daily bond-buying operations, aimed at pouring money into the financial markets and lowering Japan's long-term interest rates in an attempt to shore up investment and consumption, have often affected foreign-exchange developments.