In a blow to Prime Minister Shinzo Abe's security reform bills, two former heads of the government bureau responsible for interpreting the pacifist Constitution criticized the proposed legislation Monday — with one slamming them as unconstitutional.

The criticism by two former officials who once oversaw national legislation and provided legal advice to the Cabinet could prove a headache for the administration after noted constitutional scholars already raised doubts in the Diet in early June about the constitutionality of Abe's flagship bills.

Testifying before a special Diet committee, Reiichi Miyazaki, who headed the Cabinet Legislation Bureau from 2006 to 2010, called for the bills to be scrapped, saying that exercising the right to collective self-defense would "go against (the Constitution's war-renouncing) Article 9."