The Asian Football Confederation said Thursday it has rejected a Kawasaki Frontale appeal over sanctions issued after the Japanese club's fans raised a controversial wartime Japanese flag during an Asian Champions League match in South Korea earlier this year.

The AFC fined Kawasaki $15,000 and placed the J-League club on one-year probation in May over the incident, which took place during their 1-0 win at Suwon Bluewings on April 25.

The confederation said Kawasaki would automatically be forced to play one game behind closed doors and be subject to more severe punishment if the flag reappears during the probationary period.

Frontale insisted the flag "did not have any political or discriminatory undertones."

During the ACL match, two Frontale supporters waved the 16-ray rising sun flag, nearly provoking a postgame riot.

Kawasaki officials confiscated the flag from the two fans and had to escort other supporters out of the stadium.

The flag was used by the Imperial Japanese Army during World War II. Although it is still flown by the Japan Maritime Self-Defense Force, the flag is considered a symbol of Japan's wartime aggression in many Asian countries, including South Korea and China.