TOKYO (Kyodo) -- Prime Minister Shinzo Abe filed his candidacy on Friday for a ruling party leadership election, in a two-way race for the top post he has been holding since 2012 against former Defense Minister Shigeru Ishiba.
Abe is widely predicted to win the Liberal Democratic Party's Sept. 20 leadership contest, which will effectively decide Japan's next prime minister.
The expected victory with the backing of a majority of LDP lawmakers would give him another three-year term and an opportunity to become Japan's longest-serving prime minister.
The 63-year-old prime minister has already secured support from more than 80 percent of all 405 LDP lawmakers.
Ishiba is trying to widen his support base among LDP lawmakers who have been frustrated with Abe's way of handling the government over nearly six years and rank-and-file party members, in particular those living in rural regions.
"By debating with (LDP) President Abe, I hope this leadership race will present options for the country's people," Ishiba told reporters.
Despite the start of electioneering, Abe and Ishiba have decided to refrain from carrying out campaign activities for a few days following the deadly earthquake that hit Hokkaido on Thursday.
A joint press conference by Abe and Ishiba, originally scheduled for Friday, will take place on Monday.
A debate session to be sponsored by the Japan National Press Club is expected to be held on Sept. 14, instead of Saturday as initially planned.
Next week, Abe is scheduled to travel to Russia to attend an annual economic forum and plans to hold bilateral talks with Russian President Vladimir Putin and Chinese President Xi Jinping.
Abe was re-elected unopposed as head of the party in 2015 when his second term ended. Six years ago, he beat Ishiba in a runoff after coming second behind him in the first round of voting.
Known as a security hawk, Ishiba, 61, has assumed other key posts, including minister in charge of regional revitalization and LDP secretary general under Abe.
A major issue in the election is whether the war-renouncing Article 9 of the Constitution should be revised.
The two conservative lawmakers have different approaches to the issue.
Abe, who is eager to realize a first-ever amendment to the pacifist Constitution, has proposed clarifying the legal status of the Self-Defense Forces in Article 9 to bring an end to arguments made by some scholars that the Japanese troops are "unconstitutional."
Article 9 of the supreme law renounces war. But the government has maintained the position that the forces are constitutional as it has interpreted the article as not banning Japan from possessing the "minimum necessary" capability to defend itself.
Abe said the LDP should submit constitutional revision proposals to an extraordinary Diet session expected to be convened this fall.
Ishiba has insisted that rewriting Article 9 should not be rushed, citing a lack of public understanding. He instead calls for changing the Constitution on points such as giving the government unilateral power to issue ordinances in cases of natural disasters and other emergencies.
On the economic front, Abe has touted the achievements of his "Abenomics" policy package, including upbeat corporate performances, especially those of large companies, and increasing job availability.
Ishiba, who represents a constituency in Japan's least-populated prefecture of Tottori, has said regional economies have not benefited from Abe's policies and new steps are needed to boost them.
As for foreign affairs, Abe is expected to stick with his policies, including maintaining close ties with U.S. President Donald Trump and a hardline stance against North Korea.
Japan has never had diplomatic relations with North Korea. Ishiba has proposed establishing a liaison office in Pyongyang that would have the task of negotiating with North Korea to secure the return of Japanese nationals it abducted in the 1970s and 1980s.