TOKYU (Kyodo) -- Japanese Prime Minister Shigeru Ishiba is considering visiting South Korea in early January for talks with President Yoon Suk Yeol, diplomatic sources said Thursday.

The planned trip will be part of their "shuttle diplomacy," or regular mutual visits, resumed between Tokyo and Seoul in 2023 before the 60th anniversary of the normalization of their ties next year.

Since taking office on Oct. 1, Ishiba has held in-person talks with Yoon twice on the fringes of international conferences, agreeing on closer bilateral and trilateral collaboration also involving the United States.

In November, the two leaders shared "serious concern" over North Korea's nuclear and missile activities as well as its military cooperation with Russia including Pyongyang's recent troop deployment to help Moscow's war against Ukraine.

Japan-South Korea relations had deteriorated to the worst level in decades over the compensation for what Seoul says was forced labor during Japanese colonial rule of the Korean Peninsula from 1910 to 1945, among other history and territorial issues.

But the relationship has since improved after Yoon, who took office in 2022, announced a solution to the wartime labor issue last year amid growing common security concerns such as North Korea and China.

In March last year, Yoon held a summit with then Japanese Prime Minister Fumio Kishida, becoming the first South Korean leader to visit Japan in nearly four years.

Ishiba's planned visit comes after South Korean officials skipped an event Sunday on Japan's Sado Island to commemorate Japanese and Korean victims who worked at a gold and silver mine complex. It was added to UNESCO's World Heritage list in July.

South Korea initially objected to the listing, citing links to wartime forced labor but later agreed after Japan pledged to hold annual memorial events.

Regarding its absence at Sunday's ceremony, South Korea said the contents of the event failed to reach the level the two countries had agreed on.

On Tuesday, the two countries' foreign ministers met and affirmed to work together to prevent the issue from disrupting diplomatic ties.