Japan and South Korea remained at odds during bilateral ministerial talks over the weekend over Seoul’s call for Tokyo not to fly the Rising Sun flag, which was also used during World War II, at a naval review held in South Korean waters earlier this month.

“It is extremely unfortunate that Japan’s Maritime Self-Defense Force had to cancel its participation due to the unacceptable (request),” Defense Minister Takeshi Iwaya told his South Korean counterpart, Jeong Kyeong Doo, at the outset of a meeting Saturday in Singapore that was open to the media.

In response, Jeong said it was “regrettable” that Japanese ships could not take part in the international naval event held off South Korea’s southern Jeju Island.

In August, South Korea told Japan and other countries that during the review, their naval ships should only fly their national flag and that of South Korea.

Japan withdrew because of that request, saying its vessels are required by domestic law to fly the Rising Sun flag. It also noted that the flag has long been recognized under international law as indicating that a vessel is Japanese.

The Rising Sun flag was used by the Imperial Japanese Army and Navy during World War II, and is thus regarded in South Korea and China as a symbol of Japan’s wartime aggression.

In the talks, Iwaya criticized South Korea for letting its ships and those of some other countries fly banners other than their national flags during the naval review, according to a Japanese Defense Ministry official.

Jeong was appointed South Korean defense chief last month, and Iwaya as the Japanese defense minister this month.

They held talks for the first time on the sidelines of a major security meeting in Singapore between the defense chiefs of the 10 member states of the Association of Southeast Asian Nations, and of eight regional partners.

In the talks, Iwaya and Jeong agreed to maintain close communication, as the two countries are working together on issues such as compelling North Korea to abandon its nuclear weapons.

“We’ve agreed to strengthen communication between our countries’ defense authorities further, overcome difficult problems and develop defense cooperation and exchanges in a future-oriented fashion,” Iwaya told reporters.

The Japanese and South Korean defense chiefs met with U.S. Secretary of Defense Jim Mattis on Friday, where they agreed to jointly work to ensure U.N. sanctions against North Korea are strictly enforced.