The United States under the Joe Biden administration is set to boost trilateral cooperation with its allies, South Korea and Japan, to keep a rising China in check.

But this would require its two partners to first mend their ties, which have sunk to new lows over historical and trade issues.

Experts said the road ahead will be bumpy as spats deeply rooted in history are hard to resolve, although meaningful progress is possible this year if the two sides can agree that it is time to move on.

South Korea has already made a series of conciliatory moves such as describing Japan as its "closest neighbour" in its latest diplomatic White Paper. President Moon Jae-in has also acknowledged that liquidating the assets of Japanese companies embroiled in a wartime forced labour dispute was "not desirable" for bilateral ties.

Yet Tokyo remains aloof, uninterested in talks with South Korea's newly appointed Foreign Minister Chung Eui-yong or its envoy in the Japanese capital, Mr Kang Chang-il.

Analysts said it will take more than just lip service to appease Japan, which insists that all historical issues have been settled under the 1965 treaty that normalised bilateral relations and has urged Seoul to take action first to resolve the forced labour issue.

A long-running spat over wartime sexual slavery also continues to bedevil ties. The issue was supposed to have been settled in a 2015 "final and irreversible" bilateral agreement, but the Moon government that came into office two years later has insisted it is flawed as it ignored the victims' demands.

Professor Kan Kimura from Kobe University's Graduate School of International Cooperation Studies said the Japan-Korea conflict is hard to resolve as both countries strongly believe in their own historical perspectives and do not want to make any concessions.

In fact, a recent survey showed that a record 40.4 per cent of respondents in Japan saw ties with South Korea as "not important".

He also noted that judicial decisions in both countries are divided and it will be tough for the governments to take any actions that are contrary to court rulings. Japan's Supreme Court has ruled that all issues with Seoul were resolved under the 1965 treaty, while South Korea's Supreme Court in 2018 ordered Japanese firms to compensate forced labour victims, and a lower Seoul district court last month allowed 12 former comfort women to seek compensation from Japan.

"It is extremely difficult for either side to compromise due to the domestic political processes," Prof Kimura told The Sunday Times. "Hence, the only way to overcome this situation is through the help of a third party."

In this sense, mediation by the Biden administration could nudge both sides towards reconciliation.

"I don't think the Suga administration will be so stubborn as to refuse dialogue so strongly," said Prof Kimura, referring to Japanese Prime Minister Yoshihide Suga.

"Japan and South Korea will, under US pressure to improve relations, observe the situation and prevaricate until Washington demands concrete trilateral cooperation on issues such as China and North Korea."

In Seoul, Dr Shin Beom-chul of the Asan Institute for Policy Studies said there is urgency for the Moon administration to mend ties with Japan in exchange for US support for the top issue in its diplomatic agenda - the resumption of nuclear talks with North Korea before Mr Moon's term ends in May next year.

"Moon wants the US to prepare to address the North Korean issue as soon as possible, but the US will probably demand that the South Korean government take some necessary measure to improve Korea-Japan relations first," said Dr Shin.

The South Korean government may also have realised that it will need Japan's support in dealing with Pyongyang.

Ewha Womans University's associate professor of international studies Leif-Eric Easley said: "If ties with Tokyo remain strained, Seoul may lose valuable input on Washington's policies towards North Korea and China."

He suggested that Mr Moon could express an intention to improve ties with Tokyo in his speech tomorrow, March 1, which marks a major independence movement against Japanese colonial rule.

Seoul can then reinstate the Reconciliation and Healing Foundation - which was dismantled in 2018, two years after it was established - to support victims of sexual slavery in accordance with the 2015 agreement. Another fund can be set up to support forced labour victims and settle claims arising from court cases in South Korea.

"Once Tokyo sees that state immunity will be respected and Japanese assets will not be liquidated, bilateral talks for harmonising export control regulations should proceed apace, allowing for the removal of the summer 2019 trade restrictions," Prof Easley said.

Another way to move forward is for both Seoul and Tokyo to agree to put aside the historical disputes and focus on cooperation instead, said law professor Lee Jae-min of Seoul National University. This can include cooperation on trade, the Covid-19 pandemic and the new digital economy, he added.

"The most practical way is to leave aside all the thorny issues for now and try to find some grounds for compromise to rebuild trust and cooperative spirit," Professor Lee said in an interview.

"The restoration of relations is important for both Korea and Japan, and there can be meaningful development on that front this year. The two sides have to agree not to worsen the status quo, to leave their differences for now, and focus on cooperation."