Prime Minister Shigeru Ishiba sounded cautious Sunday about expanding the ruling coalition between his Liberal Democratic Party and Komeito.

"A coalition should be formed after a certain level of agreement is reached on diplomacy, security and public finances," Ishiba said in a speech ahead of Thursday's start of the official campaign period for the July 20 election for the House of Councilors, the upper chamber of Parliament.

At a conference hosted by a private policy proposal group, Ishiba also expressed support for the idea of establishing a nonpartisan consultative body on social security reform.

On measures against persisting inflation, he stated, "What is needed now is immediate effects," reiterating the need to provide a cash benefit of ¥20,000 to ¥40,000 per citizen, included in his party's election pledges.

"We must secure financial resources for medical care, elderly care and pensions," he said, indicating a negative view about opposition proposals for lowering the consumption tax.

At the conference, opposition party leaders expressed skepticism about joining the coalition.

"It's impossible to form a grand coalition just with one issue," Yoshihiko Noda, president of the main opposition Constitutional Democratic Party of Japan, said adding that a coalition with the LDP "would not be easy."

Hirofumi Yoshimura, leader of Nippon Ishin no Kai (Japan Innovation Party), declared, "We have no intention of joining the (LDP-Komeito) coalition."

In contrast, Yuichiro Tamaki, leader of the Democratic Party for the People, refrained from taking a position, saying that things would depend on the Upper House election results.

Komeito leader Tetsuo Saito stated, "Now is not the time to think about any partner other than the LDP and Komeito."

Noda and Yoshimura, Osaka governor, approved the idea of setting up the consultative body for social security reform. They also called for a temporary consumption tax cut for food.

Japanese Communist Party leader Tomoko Tamura said that the consumption tax rate be lowered to 5%.