Japanese government officials expressed concerns Saturday that the ongoing political turmoil in South Korea may derail improving relations between the two countries.

The administration of South Korean President Yoon Suk Yeol could be a "lame duck," a Japanese Foreign Ministry source said, even though Yoon survived an impeachment motion over his short-lived declaration of martial law that triggered condemnation from lawmakers and the public.

The motion was scrapped due to a lack of the required number of voters in parliament.

"We may go back to the days where bilateral relations worsened," the source said.

Prime Minister Shigeru Ishiba is planning to visit South Korea in January, but at present that trip is doubt, Japanese sources said.

Yoon, who took office in 2022, has led efforts to improve relations with Japan including agreeing on a solution regarding compensation demands from South Koreans over wartime labor during Japan's 1910-1945 colonial rule of the Korean Peninsula.

The Japanese government is concerned that growing criticism of Yoon within South Korea may trigger a strong backlash against policies the president has taken.

Another government source expressed hope that "Japan-South Korea relations will not become part of the contentions between the ruling and opposition parties" in South Korea.

A separate government source was wary over the impact of the situation in South Korea on the three-way coordination between Japan, South Korea and the United States in confronting North Korea's nuclear and missiles development.

With South Korea experiencing political upheavals, "there is a possibility that previous agreements (between the three countries) may be overturned. For now we just need to watch cautiously," the source said.