Photo/Illutration Indonesia’s Adm. Yudo Margono, center, talks with Cambodia’s Gen. Vong Pisen, second right, Thailand’s Gen. Chalermphon Srisawasdi, third left, and Vietnam’s senior Lt. Gen. Nguyen Tan Cuong, left, during the Association of Southeast Asian Nations (ASEAN) chiefs of defense forces meeting in Nusa Dua, Bali, Indonesia on June 7, 2023. (AP Photo)

JAKARTA--The Association of Southeast Asian Nations is moving ahead with plans for joint naval exercises in September, the first held by countries in the bloc on their own, at a time when several are responding more strongly to increasing Chinese assertiveness in the area.

The Indonesian military said Tuesday that ASEAN member countries held an initial planning conference for the joint exercises, to be held Sept. 18-25 near a disputed area of the South China Sea, despite skepticism from Cambodia.

China says the vast majority of the South China Sea lies within its “nine-dash line,” which it uses to demarcate what it considers its maritime border. That has brought it into tense standoffs with the ASEAN nations of Indonesia, Vietnam, Malaysia, Brunei and the Philippines, with Chinese fishing boats and military vessels becoming more aggressive in the disputed waters.

Indonesia’s military chief, Adm. Yudo Margono, initially said the exercises would take place in an area of the South China Sea which Indonesia renamed the North Natuna Sea in 2017 to underscore its claim that the area, which includes natural gas fields, is part of its exclusive economic zone. Similarly, the Philippines has named part of what it considers its territorial waters the West Philippine Sea.

In a statement Tuesday, however, Indonesia, which holds the rotating chair of ASEAN, said the exercise is now being planned for the waters of South Natuna, just outside the nine-dash line.

ASEAN members Cambodia and Myanmar, which maintain close ties with China, declined to take part in the planning conference, according to the Indonesian military.

After Indonesia announced the exercises earlier this month following meetings of defense officials in Bali, Cambodia denied that anything had been decided, issuing a statement that it had been asked to join a military drill and was establishing a working group to look into it.

Cambodia’s Defense Ministry did not immediately respond to a request for comment on the revised plan for the exercise.

China has in the past explained its presence in disputed waters on the basis of what it said were its “traditional fishing rights.” Chinese ships also regularly patrol off the island of Borneo and near James Shoal, east of the Natuna islands, which is China’s southernmost territorial claim and is also claimed by Malaysia.

In one well-publicized incident, a Chinese coast guard ship on Feb. 6 aimed a military-grade laser at a Philippine patrol boat off a disputed reef, temporarily blinding some crew members and prompting Manila to intensify its patrols in the disputed waters.

ASEAN nations have taken part in naval exercises before with other countries--including both the United States and China--but the September drills would be the first involving just the bloc and are being read by many as a signal to China.

Teuku Rezasyah, an international relations expert at Indonesia’s Padjajaran University, said Indonesia needs to explain in detail what it is planning in order to avoid any misunderstandings about what message, if any, it might be trying to send to Beijing.

“This must be explained to the public, because if not, it will give the impression that we are taking actions that will make China unhappy,” he said. “The navy moving around the Natuna Sea will give the impression we are harassing China’s nine-dash line.”