Former Bank of Japan Gov. Masaaki Shirakawa expressed concern at a policy meeting in 2012 about the central bank's possible adoption of a 2% inflation target, shortly before the goal was enshrined in a joint statement with the government, minutes showed Tuesday.

"Is it really achievable in a decent amount of time?" Shirakawa was quoted as saying at the BOJ's policy meeting in December 2012. The inflation target was subsequently adopted in a joint statement with the government led by then Prime Minister Shinzo Abe, known for his "Abenomics" economic program.

The newly disclosed minutes of the bank's policy meetings between July and December of that year show how skeptical Shirakawa was about the effectiveness and prospect of achieving the target, which remains elusive for Japan a decade after its introduction in 2013.