Reuters reports that board member Takako Masai said that the Bank of Japan must deepen debate on how to address the rising cost of prolonged monetary easing, such as by making its purchases of exchange-traded funds (ETF) more flexible.

With the coronavirus pandemic likely to keep Japan's economic recovery moderate, the central bank must seek ways to make its policy framework sustainable, she said.

The need to enhance the effect of its monetary tools has also heightened because cutting already low interest rates will likely give a limited boost to growth, Masai said.

"The BOJ's ETF buying, along with forward guidance, will remain among tools to enhance the effect of monetary easing," Masai told a news conference.