Japanese Prime Minister Shigeru Ishiba on Wednesday denied media reports of his planned resignation, reiterating his intention to remain in office and emphasizing the need to swiftly address policy challenges, including implementing the recently reached tariff agreement with the US, NHK reported on Wednesday afternoon.

Since the crushing defeat in Sunday's upper house election, speculation about Ishiba's political future has been fluctuating wildly. On Monday, he announced his intention to remain in office, only for Japanese media including the Mainichi Shimbun on Wednesday morning to report his intention for resignation by the end of August - a claim he personally denied that same afternoon, according to Japanese media reports.

This came as the US and Japan struck a deal to lower the hefty tariffs Washington threatened to impose on goods from its Asian ally that included a pledge by Japan to invest $550 billion in the US, Reuters reported on Wednesday.

Mainichi reported, on Wednesday, the Japanese prime minister held talks with Liberal Democratic Party (LDP)'s senior advisor Taro Aso, vice president Yoshihide Suga, and former prime minister Fumio Kishida, where discussions were believed to have centered on his political future.

According to the report, after the upper house election defeat, calls for Ishiba's resignation and criticism within the party are mounting-although he initially expressed his intention to stay in office following the LDP's crushing defeat in the upper house election on Sunday- the timing of his final decision could still change.

In response to Ishiba's political future and its impact over China-Japan relations, Guo Jiakun, spokesperson for the Chinese Foreign Ministry, stated at a regular press briefing on Wednesday that "This is Japan's internal affair and I have nothing in particular to say."

The Chinese spokesperson stated that China and Japan are close neighbors. It serves the fundamental interests of both countries and peoples to maintain the sound and steady development of bilateral relations, make joint effort to comprehensively advance the strategic relationship of mutual benefit and build a constructive and stable China-Japan relationship fit for the new era, Guo said.

Mainichi Shimbun reported that, on Wednesday, when asked by reporters at the prime minister's office about how the recently reached US-Japan tariff agreement - one of the reasons he had cited for staying in office - might affect his decision on whether to remain, Ishiba stated: "I cannot comment until we have thoroughly examined the details of the agreement."

Reuters reported on Wednesday that the US and Japan struck a deal to lower the hefty tariffs Washington threatened to impose on goods from its Asian ally that included a pledge by Japan to invest $550 billion in the US.

The agreement - including a 15% tariff on all imported Japanese goods, down from a proposed 25% - is the most significant of the string of trade deals the White House has reached ahead of an approaching August 1 deadline for higher levies to kick in, Reuters noted.

When asked by Reuters about US-Japan trade deal, Guo said Wednesday that "China, as always, believes that all parties should solve economic and trade disagreements through equal-footed dialogue and consultation, and uphold a sound environment for international trade and economic cooperation."

This agreement is the result of prolonged and intense negotiations, Jiang Yuechun, senior research fellow and director of the Department for World Economy and Development Studies, China Institute of International Studies, told the Global Times on Wednesday. "While the agreement exhibits some asymmetries, its terms are broadly acceptable to both sides," Jiang said.

Jiang analyzed that in the near term, the agreement helps ease bilateral trade tensions and mitigates further economic damage. The bullish Japanese stock market reflects optimism over de-escalation, the expert said.

According to CNN on Wednesday, the deal saw Japanese markets hit a one-year high on Wednesday, with a surge in the price of automaker shares pushing the Nikkei 3.7% higher.

However, Jiang warned, the deal leaves structural disputes in auto trade unresolved, as Japan's market barriers against US cars persist, risking future friction. Long-term concerns include accelerated industrial hollowing-out in Japan under US pressure to relocate core production capacity that could trigger manufacturing outflows.

From a geopolitical standpoint, at its core, the deal represents an exchange of Japan's economic concessions for US security assurances, Jiang believes. Yet this transactional dynamic also exposes structural contradictions in the alliance - Japan's growing economic reliance on the US market complicates its political autonomy, Jiang commented.

The US-Japan tariff dispute is not primarily driven by economic factors but rather by Washington's attempt to tighten its control over Tokyo, Lü Chao, an expert at the Liaoning Academy of Social Sciences, told the Global Times on Wednesday. 

The expert pointed out that unlike China, which has a strong domestic market and self-sustaining economic system, Japan has very little room to maneuver on tariff issues. This carrot-and-stick approach has already succeeded in tightening the US grip on Japan, Lü remarked.

Following the historic defeat in the upper house election, Japan's political landscape is undergoing shifts. Pro-American forces within the LDP will likely further leverage US economic pressure to expand their power, Lü believes.

According to the expert, at the same time, Japan's opposition parties are difficult to form a unified front force capable of overthrowing the LDP and establishing a new political alignment. The LDP will also strive to recover from its setback. "In this context, the pro-American faction within the LDP is likely to be the biggest beneficiary," Lü said.

Chen Xingyu contributed to this story.