The ruling Liberal Democratic Party is arranging to hold its presidential race on Sept. 20, with party President and Prime Minister Shinzo Abe seeking to win a third term to become Japan's longest-serving leader, party lawmakers said Thursday.

The LDP is expected to formally decide on the schedule in late August to start the official campaign on Sept. 7.

The conservative party decided last year to extend the term limit on party leaders to three consecutive three-year terms from the previous two consecutive three-year terms, effectively enabling Abe to remain in the post until September 2021.

Abe is expected to announce his candidacy on July 22 when the current regular Diet session ends. The Diet decided on the extension on Wednesday to ensure the passage of key bills.

The leadership race could be tough for Abe, as opposition parties continue grilling the premier over favoritism allegations leveled at him, which prompted his approval ratings to tumble before rebounding slightly recently.

Former LDP Secretary General Shigeru Ishiba, the party's policy chief Fumio Kishida and Internal Affairs and Communications Minister Seiko Noda are viewed as possible candidates.

(From left, Fumio Kishida, Shigeru Ishiba and Seiko Noda)

The leadership election will be held between two major international events Abe plans to attend -- the Eastern Economic Forum in Russia's Far East city of Vladivostok and the U.N. General Assembly gathering in New York to be held in mid- and late September respectively.

Some lawmakers said the leadership contest should be convened before the Russian forum in which North Korean leader Kim Jong Un may take part.

The Japanese prime minister is seeking to meet with Kim in an attempt to resolve the longstanding issue of Japanese nationals abducted by North Korea decades ago.

But a senior lawmaker told reporters the presidential election would not be brought forward.

Abe, if re-elected, is set to deliver a speech at the U.N. headquarters. Another party member said a new leader "who won confidence" through the leadership race should participate in the international gathering.

Abe returned to power in late 2012 after previously serving as the premier and LDP president between 2006 and 2007. His current second-term tenure is set to expire on Sept. 30.