The loss on Sunday left the Liberal Democrats a minority party in both houses of Parliament, while two new nationalist parties surged.

Sanseito leader Sohei Kamiya's xenophobic views, antisemitic remarks and emphasis on Japan’s ethnic purity have raised alarms.

The Yomiuri report comes just hours after U.S. President Donald Trump announced a trade deal with Japan, which will see the Asian economic giant subject to a 15% tariff. Ishiba welcomed the deal, having earlier signaled that he would remain in office at least until a trade agreement with the U.S. was reached.