Opposition lawmaker Denny Tamaki, who was reportedly designated as a successor by Okinawa's late governor and anti-U.S. base activist Takeshi Onaga, on Wednesday formally declared his candidacy in the gubernatorial election next month.

Tamaki, 58, a House of Representatives member of the Liberal Party, is set to face off against Atsushi Sakima, 54, a former Ginowan mayor who is backed by the Liberal Democratic Party led by Prime Minister Shinzo Abe, who has been promoting the controversial relocation of a U.S. military base within the prefecture.

The gubernatorial election will be held on Sept. 30 following the death of Onaga on Aug. 8.