South Korea has taken its complaint over Japan's refusal to ban the Rising Sun Flag at the Tokyo 2020 Olympic Games to the International Olympic Committee (IOC).
The country's Sports Ministry said it had written personally to IOC President Thomas Bach to express its "deep disappointment and concerns".
It comes after Tokyo 2020 organisers confirmed to insidethegames that they will not be banning the flag as they do not consider it to be a political statement.
"We explained the history behind the flag and asked that it be banned during the Olympics," the Sports Ministry said, according to South Korean news agency Yonhap.
The Rising Sun Flag is not Japan's national flag but is still used in Japanese society.
Its association with the military means it is viewed by some overseas as a symbol of the country's aggression leading up to and during the Second World War.
Japan conquered large parts of Asia, including the entire Korean peninsula, before their surrender in 1945.
According to Yonhap, the Sports Ministry told the IOC that the flag should be compared to the swastika symbol used in Nazi Germany.
They said the Rising Sun Flag was used in Japan by "extreme right-wing organisations" and in "xenophobic demonstrations".
The IOC Olympic Charter declares that "no kind of demonstration or political, religious or racial propaganda is permitted in any Olympic sites, venues or other areas".
But a Tokyo 2020 spokesman told insidethegames: "The rising sun flag is widely used in Japan.
"It is not considered to be a political statement, so it is not viewed as a prohibited item."
World football governing body FIFA has opted to ban the flag.
"We stressed that the use of the Rising Sun Flag at the Tokyo Olympics will directly run counter to the Olympic spirit and values of promoting world peace and love for humanity," the Sports Ministry added.
"We asked for an active role [by the IOC] to ensure the flag won't be allowed at venues."
The Korean Sport and Olympic Committee will continue to pressure Tokyo 2020 organisers over the issue, Yonhap said.
South Korea's complaint comes at a time when relations with their historical rival Japan are tense.
A trade war has developed between the countries with both restricting the other's products in a series of retaliatory measures.
The Koreans have also expressed concerns about food from Japan's Fukushima region being served during Tokyo 2020.
Fukushima was struck by one of the worst natural disasters ever to hit Japan, in 2011, when a devastating earthquake and tsunami caused an accident at a nuclear power plant.
Around 16,000 people lost their lives.
The Koreans have also threatened to review their pre-Tokyo 2020 training camp plans due to apparent fears over "radioactivity" from the region.
Further tension was felt over the appearance of a disputed territory on the official Tokyo 2020 Torch Relay map.
The map on the official website for next year's Games includes the Liancourt Rocks, which are governed by South Korea but claimed by Japan.
On August 15, South Korean protesters tore a huge Rising Sun Flag to shreds during a rally marking the anniversary of the country's liberation.
insidethegames has asked the IOC for comment.