Speeding up the Bank of Japan's purchases of Japanese government bonds would risk further distorting the world's second-biggest sovereign debt market, said Yuri Okina, vice chairman at Japan Research Institute.

"If additional easing is done using government bonds, it may have the considerable side-effect of impairing the functioning of the market," Okina, an economist and a former BOJ official, said on Feb. 26 in an interview in Tokyo. "It will probably be difficult for the BOJ to boost the pace that it buys government bonds."

Gov. Haruhiko Kuroda told the Diet last month that JGB liquidity hadn't fallen particularly as a result of the purchases. He has also said the BOJ has "many options" and may need to get creative with any further monetary stimulus. Primary dealers responsible for distributing JGBs to investors told the government in November it was getting harder to determine prices because net supply was low.