Although China was barely mentioned on the trips, pundits said Beijing was increasingly wary of its two neighbours’ warming ties and their strategic pivot towards Washington.

Liu Jiangyong, an expert on regional affairs at Beijing’s Tsinghua University, said it remained to be seen how long the rapprochement between Japan and South Korea would last, but their close military and security ties with the US was deeply worrying.

“The warming Japan-South Korea ties may impede China’s efforts to improve trilateral cooperation and have negative implications on China’s bilateral ties with both countries,” he said.

“This is because both Japan and South Korea are under pressure from Washington to help contain China and the strengthening of the US-Japan-South Korea security ties is clearly aimed at countering China, Russia and North Korea.”

During his visit to Seoul, the first by a Japanese leader to the South Korean capital in 12 years, Kishida fell short of offering a new apology over the contentious forced labour issue during Japan’s 1910-45 colonial rule of the Korean peninsula.

Instead, he said his government inherited the stance of earlier administrations, some of which had issued apologies.

“For me personally, my heart hurts when I think of the many people who endured terrible suffering and grief under the difficult circumstances of the time,” he said after his summit with Yoon on Sunday.

Yoon said unresolved historical issues should not mean that no forward steps could be taken to deepen ties.

While Washington welcomed the commitments, the pledges drew criticism in South Korea, including the country’s main opposition Democratic Party, which accused Yoon of being submissive, “oblivious to history”, and engaging in “humiliation diplomacy”.

“Why should the prerequisite for restoring bilateral diplomacy be giving up on our history,” party spokeswoman Kang Sun-woo said, according to Yonhap news agency.

What to know about South Korea-Japan ties as Yoon, Kishida meet

Shi Yinhong, a professor of international affairs at Renmin University in Beijing, said it was a major surprise to see how rapidly South Korea under Yoon had managed to catch up with the US and Japan on several critical issues to China, such as Taiwan, South China Sea and Ukraine.

“The US is set to continue to push for a trilateral military alliance, while trying to alienate South Korea’s relations with China, which have been hit by a spate of diplomatic rows and economic sanctions over the years,” he said.

“But given the negative perceptions towards each other in both South Korea and among Japan’s right-wing conservatives, and the many unresolved bilateral issues, there is still a long way to see South Korea and Japan move even closer.”

Shi said that unlike Tokyo, which had become Washington’s top ally in confronting Beijing, Seoul remained cautious in taking on its neighbour directly.

Benoit Hardy-Chartrand, an international affairs specialist at Temple University Japan in Tokyo, also said it would be foolish for both Seoul and Tokyo to be overconfident about their relationship despite the normalisation of ties.

“The return of shuttle diplomacy and regular visits as well as stronger trilateral cooperation with the United States will undoubtedly contribute to all three countries coordinating and calibrating their approaches to shared regional and global concerns,” he said.

“Nonetheless, the normalisation is liable to the vagaries of the domestic political situation in South Korea.

“The rapprochement currently benefits from the presence of a South Korean leader who was keen from the very beginning of his administration to place South Korea-Japan relations on firmer ground, but given the lingering anti-Japan sentiment in South Korea and the tendency for politicians to exploit it, the situation could easily change with the next administration.”

While Yoon and Kishida did not mention points of friction with China, they agreed to cooperate on chips, without elaborating on what the partnership would entail.

During their talks on Sunday, they confirmed that the two nations would join hands to tackle growing security threats in East Asia. They also spoke about shared values for human rights, rule of law, and a free and open Indo-Pacific.

Japan said in March that it would expand restrictions on exports of 23 types of leading-edge chipmaking technology, even as its trade officials repeatedly said it was not targeted at China.

Yoon has also been a supporter of Washington’s Asia strategy, including US President Joe Biden’s initiative to restructure global supply chains to reduce dependence on China, especially in the lead-up to his visit last month to the White House.

Chinese analysts were particularly worried about the pair’s planned trilateral summit with Biden on the sidelines of the Group of Seven summit in Kishida’s hometown of Hiroshima this month. Kishida has invited Yoon to the summit as an observer.

“The US, South Korea and Japan are in the same bed and each has its own needs and uses each other,” said Liu of Tsinghua University.