Two founding members of Tomin First no Kai (Tokyoites First), a regional party effectively led by Tokyo Gov. Yuriko Koike, plan to abandon the party on Thursday citing frustrations over the closed nature of top management, sources said.

Shun Otokita and Reiko Ueda, both members of the Tokyo Metropolitan Assembly, are among the three key assembly members who first supported Koike when she entered the office in August last year.

Otokita had served as secretary-general of the party and was once considered one of Koike's closest allies.