The ruling Liberal Democratic Party's close links with the religious group were revealed after the killing of former premier Shinzo Abe, and have been cited by public opinion poll respondents as a reason behind Kishida's low approval ratings.

Opposition parties have accused Akiba of involvement in election law violations and of ties with the Unification Church, although Akiba has denied any wrongdoing.

"There was not a single thing that I did that breached the law," Akiba said to reporters gathered at the prime minister's office after he submitted his resignation to Kishida.

"It was a difficult decision to make, but I tendered my resignation to the prime minister as I felt I must not hamper the debates in parliament," he added.