A “threat assessment” linked to Thailand following deadly land border clashes has pushed Cambodia to ratify a major United Nations maritime treaty, analysts have said.
Concerns that the Thai navy could potentially restrict supply routes in the Gulf of Thailand also played a significant role in Phnom Penh’s decision, according to experts.
Cambodia ratified the UN Convention on the Law of the Sea (Unclos) on January 16, more than 40 years after signing the treaty, making it the last member of the Association of Southeast Asian Nations (Asean) to do so.
The ratification was approved during the fifth session of Cambodia’s National Assembly and will now be forwarded to the Senate for final endorsement.
Cambodia signed Unclos in 1983, a year after the convention was adopted in Jamaica. However, the treaty only came into force in 1994, largely due to objections from industrialised countries over provisions governing deep seabed mining.
The convention is a multilateral treaty developed under the United Nations and emerged from the Third United Nations Conference on the Law of the Sea, which took place between 1973 and 1982.
Local media report that Unclos provides Cambodia with a comprehensive framework for maritime governance and legal protection under national maritime law. It also enhances the country’s standing in international forums and in addressing maritime disputes with other states.
The decision to ratify the treaty factored in Cambodia’s “threat assessment” of Thailand, said Abdul Rahman Yaacob, a non-resident senior fellow at independent think tank Verve Research.
Relations between the two Southeast Asian neighbours deteriorated last year after several deadly skirmishes, largely stemming from a long-standing and unresolved border dispute, worsened by heightened nationalist sentiment and security anxieties.
Following the clashes, speculation emerged that Thailand’s navy might seal off the Gulf of Thailand, potentially cutting Cambodia’s maritime supply routes, a claim Bangkok has denied.
“Cambodia could attempt to use Unclos as a reference point while negotiating with Thailand,” Rahman said.
Given Cambodia’s relatively small and less capable navy, he added that a legal framework offered an alternative means of safeguarding its maritime interests.
Cambodia’s key interests in the Gulf of Thailand include securing energy resources, maintaining access to shipping lanes and protecting fisheries.
These interests are closely tied to unresolved maritime boundary disputes with Thailand and Vietnam, particularly an overlapping claim in the Gulf of Thailand involving Bangkok.
Rahman noted that since signing Unclos in 1983, Cambodia has prioritised internal security and national cohesion.
Over that period, the country evolved from a war-ravaged state under Vietnamese occupation into a fragile constitutional monarchy following UN-backed elections in 1993, before transitioning into decades of one-man rule under former prime minister Hun Sen, marked by economic recovery and growth.
“The ratification of Unclos has not been the Cambodian government’s priority,” Rahman said.
Chong De Xian, an associate research fellow with the Maritime Security Programme at Singapore’s S. Rajaratnam School of International Studies, said Cambodia was framing the ratification as both “a governance upgrade and a positioning move”.
He explained that Unclos not only establishes a comprehensive framework for maritime law and administration, but also enables disputes to be managed in a more “rules-based” manner.
According to Chong, last year’s sharp decline in relations with Thailand, following the most serious fighting in years, had “sharpened Cambodia’s appetite to harden its positions through internationally recognised rules and to reduce exposure to bilateral volatility”.
However, Chong cautioned that ratification could complicate political dynamics if neighbouring countries interpret Cambodia’s actions as an attempt to consolidate its claims in the Gulf of Thailand ahead of formal maritime delimitation.
He said steps such as issuing new baselines, publishing official maritime charts and coordinates, tightening enforcement, or granting fishing and mining licences in disputed waters could be seen as efforts to “lock in” entitlements and “create facts” on the ground.
“That can trigger pushback and make negotiations more politically difficult,” Chong said.
Ratification would also make it “politically harder” for Phnom Penh to dismiss legal arguments based on Unclos, especially as Asean members increasingly use the convention’s legal framework “to push back against claims inconsistent with Unclos”, he added.
The Philippines and Vietnam have consistently argued that China’s maritime claims in the South China Sea violate Unclos.
In 2016, Cambodia, a close ally of Beijing, blocked Asean from issuing a joint statement referencing a Permanent Court of Arbitration ruling that invalidated China’s “nine-dash line” claims in the disputed waters.
Pou Sothirak, senior adviser to the Cambodian Centre for Regional Studies, said the prolonged delay in ratifying Unclos stemmed from “the lack of full understanding” of the treaty’s “significant usefulness”.
He said Cambodia previously viewed the convention as lacking “sufficient strength” in areas such as environmental protection, climate change adaptation, marine biodiversity conservation and regulation of deep seabed mining.
Unclos was also regarded as “relatively weak in addressing maritime security threats, resolving territorial disputes, and regulating emerging technologies”, he added.
Sothirak said these concerns were compounded by the complex legal implications of Unclos’ provisions on resolving overlapping maritime claims, particularly as disputes with Thailand could become “eminent in the foreseeable future”.
By ratifying the treaty, Cambodia has more clearly demonstrated its commitment to a rules-based international order and international law, helping to resolve a long-standing “dilemma” over whether to align fully with Asean’s Unclos-based positions or remain neutral, he said.
“As a small state, Cambodia is vulnerable to external pressures from bigger and stronger neighbours,” Sothirak said.
“[It] can now rely on [Unclos] to protect its maritime sovereignty and interests against illegal intrusions by neighbouring states with shared maritime boundaries.”
