Shigeru Yamaguchi, a former chief justice of the Supreme Court, has described Prime Minister Shinzo Abe's security bills to bolster the role of Japanese forces abroad as going against the country's pacifist Constitution.

"I would have to say the legislation to exercise the right to collective self-defense is unconstitutional," Yamaguchi said Thursday during an interview. It is the first time a former chief justice has made such a remark.

The comment comes at a sensitive time as the government and ruling camp push ahead with the legislation despite strong criticism from the public, and may, political analysts say, add to ongoing debate about the constitutionality of the bills.