A former prosecutor general and six others will form an investigative panel to determine the cause of, and the people responsible for, the government's massive pension record debacle, the Internal Affairs and Communications Ministry said Friday.

The fiasco, which has rendered at least 50 million public pension accounts unidentifiable and shortchanged an unknown number of retirees, is growing into a major hurdle for the ruling coalition ahead of the House of Councilors election in July.

The panel, set up at the direction of Prime Minister Shinzo Abe, will be chaired by former prosecutor Kunihiro Matsuo and answer to the ministry, which is in charge of administrative evaluations.