Faced with mounting challenges, Indonesia, the Philippines and Vietnam are exploring security cooperation focused on maritime order in the South China Sea. The nations are advancing a framework that reinforces Association of Southeast Asian Nations (ASEAN)-led regionalism while maintaining sovereign flexibility.
A growing network of bilateral arrangements forms the core of a trilateral relationship centered on legal clarity and operational readiness. “What we’re really seeing first is practical cooperation at sea, especially between coast guards,” Ridvan Kiliç, an Australia-based defense analyst, told FORUM. “That’s where Indonesia, Vietnam and the Philippines are finding common ground in very operational, day-to-day ways.”
A significant legal measure underpinning cooperation is an Indonesia-Vietnam agreement demarcating the nations’ overlapping exclusive economic zones (EEZ) in the North Natuna Sea. Settling the EEZ claims under the United Nations Convention on the Law of the Sea was “particularly significant because it removed a long-standing source of friction,” Kiliç said.
The legal alignment enabled Hanoi and Jakarta to expand joint coast guard activities, and in March 2025, the nations elevated ties to a Comprehensive Strategic Partnership, incorporating defense industry cooperation and officer exchanges.
Meanwhile, the Philippines and Vietnam have built mechanisms to manage tensions and reduce risks in contested waters. A 2024 joint statement gave assurances of strengthened maritime law enforcement and search and rescue cooperation, and recent defense policy dialogues have expanded to include cybersecurity, logistics and medical cooperation.
In early 2025, coast guard and fisheries personnel from Indonesia, the Philippines, the United States and Vietnam conducted a two-week maritime law enforcement course in the southern Philippines. The training focused on boarding procedures, arrest techniques, evidence handling and risk mitigation. According to the U.S. Embassy in Manila, the engagement strengthened regional coordination against illegal maritime activity.
Forums such as the ASEAN Defence Ministers’ Meeting provide complementary channels for information sharing, joint training and doctrinal coordination among Indonesia, the Philippines and Vietnam. The nations also regularly co-chair expert working groups, particularly on maritime security.
The ASEAN Coast Guard Forum — initiated by Indonesia in 2022 and hosted by the Philippines in 2024 — is a venue for advancing protocols to prevent maritime incidents.
“At the core, all three countries share an interest in upholding a rules-based maritime order,” Kiliç said. “That common legal and normative position is a quiet but powerful driver of their cooperation.”
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