Former Japanese Defense Minister Shigeru Ishiba and Former Foreign Minister Fumio Kishida on Tuesday both officially announced they will be running for the leadership of Japan's ruling party. 

Prime Minister Shinzo Abe announced his resignation on Friday due to the worsening of a chronic health condition. His Liberal Democratic Party (LDP) is expected to hold its leadership vote on September 14.

The president of the LDP is virtually assured of being prime minister because of the party's majority in parliament's lower house. 

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Ishiba is a favorite to lead the LDP in opinion polls, but the slimmed-down version of the election that officials have announced is widely expected to work against him. 

Ishiba said he regretted that ordinary party members will be unable to vote. 

Kishida, currently policy chief of the LDP said the country must focus on challenges such as poverty and social disparity. 

"I will make utmost efforts for the benefit of the nation and the people," he told a news conference, adding that he could show strength in the areas of economic and foreign policy due to his experience, which includes serving as foreign minister from 2012 to 2017. 

Other contenders in the race are Chief Cabinet Secretary Yoshihide Suga, seen as the favorite in the party. Current Foreign Minister Toshimitsu Motegi and Defense Minister Taro Kono both said on Tuesday they had not yet decided whether to run. 

(With input from agencies)