Ishiba, who secured the LDP leadership on Friday, is set to be formally appointed as prime minister on Tuesday in an extraordinary Diet session. The former defense minister is reportedly assembling his cabinet and party leadership team, with several key appointments already in consideration.
Sources close to Ishiba said he intends to dissolve the House of Representatives in October after engaging in parliamentary debates with opposition parties.
"An election should be held at the earliest possible date," Ishiba said in a television interview on Sunday, adding, "I don't deny various possibilities."
The new LDP leader is facing challenges in uniting the party post-election, as evidenced by economic security minister Sanae Takaichi's reported refusal of a key party post offer. Ishiba is expected to tap several party heavyweights for important positions, including former Prime Minister Yoshihide Suga as LDP vice president.
Japan's main opposition Constitutional Democratic Party has called for sufficient time to question the new prime minister in parliament before any election is called. The opposition also urges the government to draft a supplementary budget for reconstruction efforts in earthquake and flood-hit Ishikawa Prefecture.