The Japanese government has sent an official for the first time to a ceremony in western Japan to promote the country's claim to disputed islands in the Sea of Japan.
The islands are known in Japan as Takeshima. South Korea controls them.
Aiko Shimajiri, the Cabinet Office parliamentary secretary in charge of the Takeshima issue, attended the annual event in Matsue City, Shimane Prefecture, on Friday afternoon. She is the first Japanese government official to do so.
The South Korean Foreign Affairs and Trade Ministry warned on Thursday that it may take countermeasures if a government official attends the ceremony.
Some South Korean media outlets are speculating that Japan's government intends to elevate the importance of the prefectural event.
Others say the event may cause bilateral ties to worsen before President-elect Park Geun-hye is inaugurated on Monday.
Analysis: Japan's mission impossible: to spend $100 billion in 15 months What do you buy the nation that already seems to have everything?
That is the question facing Japanese Prime Minister Shinzo Abe as he aims to spend more than $100 billion on infrastructure in the next 15 months to help revive his country's economy. But with its gleaming bullet trains, jungles of elevated highways and strings of man-made islands, ultra-modern Japan doesn't appear to want for much.
"We cannot simply continue to build roads and infrastructure the way we used to at a time when the population is ageing and shrinking," says Takayoshi Igarashi, a public policy professor at Japan's Hosei University who has advised the previous Democrat administration on rebuilding from the 2011 earthquake, tsunami and Fukushima nuclear accident.
Infrastructure spending tops Abe's economic agenda alongside nudging the central bank into more aggressive steps to end deflation. Since he took power in December, Abe has earmarked 10 trillion yen ($107 billion) for new infrastructure and upgrades over the next 15 months - half of it funded by government debt.
That is equivalent to a quarter of the amount that the Organisation for Economic Cooperation and Development estimates the entire world needs to spend on transport infrastructure each year.