Japanese Prime Minister Shinzo Abe said Sunday that he will run in the Liberal Democratic Party's (LDP) leadership election to be held next month.

"I am determined to hold the helm of Japan for three more years as LDP president and prime minister," Abe told reporters in Tarumizu, Kagoshima prefecture, in southwestern Japan.

The election, to be held on Sept. 20, is likely to be a two-horse race between Abe and former Defense Minister Shigeru Ishiba.

The ruling party's election will essentially decide not just the LDP's leader but also who will go on to serve as the nation's prime minister.

If Abe, 63, who is currently favorite to win the race with five out of seven intraparty factions supporting him, does so, his third-term at the helm will all but ensure he becomes the longest-serving prime minister in postwar Japan.

Abe has been unopposed and was reelected for his second consecutive three-year term in 2015.

Former Defense Minister Shigeru Ishiba, 61, officially declared his candidacy on Aug. 10 and has since said that if Abe were allowed to run unopposed again, it would undermine democracy here.

Ishiba, a lower house member, has in the past been outspoken about Abe and his policies and this will be the third time for the veteran politician to attempt to win the ruling party's top post.

Official campaigning for the LDP leadership is slated to begin on Sept. 7.