The decision to join UNCLOS comes after 40 years of delays, opening a new front with Thailand over the disputed oil fields off Koh Kood Island. In 2001, then Thai PM Thaksin Shinawatra signed an agreement with his Cambodian counterpart Hun Sen, for joint exploitation, but this never materialised and is now contested by Bangkok. The issue ties in with the 2016 arbitration on China’s "nine-dash line” with which Beijing claims most of the South China Sea.

Milan (AsiaNews/Agencies) – After more than 40 years of waiting, Phnom Penh finally decided to ratify the United Nations Convention on the Law of the Sea (UNCLOS), a treaty agreed to in 1982 that establishes a global legal framework for the oceans and seas, regulating territorial waters and resource use.

Despite signing the treaty in 1983, Cambodia remained the only ASEAN country that had not ratified it. On 16 January, during its fifth session, Cambodia’s National Assembly in Phnom Penh passed a bill to this effect, and the Cambodian Senate is expected to approve it very soon.

It is not hard to see this development as a side effect of Cambodia’s conflict with Thailand, which has seen the two countries clash in recent months over the border issue, fuelled by nationalist sentiments on both sides.

The latest outbreak of fighting – which resulted in dozens of casualties on both sides – was halted by a ceasefire reached on 27 December.

But thousands of people were displaced from the areas affected by the violence, and political negotiations between Bangkok and Phnom Penh are struggling to get off the ground, partly because of Thailand’s upcoming parliamentary election on 8 February.

Against this backdrop, Cambodia's decision to ratify UNCLOS appears to be a further attempt to internationalise the crisis, focusing on the sea, another area pitting the two countries against each other.

In fact, during the height of fighting, there was talk that the Thai navy could close the Gulf of Thailand, cutting off Cambodia's sea lines of communication, a possibility Bangkok denied.

But the issue is much broader and stems from the 1907 Franco-Siamese Treaty, which did not define any maritime border between the then Kingdom of Siam and French-ruled Cambodia.

Thus, both countries have historically asserted claims to the island of Koh Kood (which is under Thai sovereignty) and, more importantly, to approximately 26,000 square kilometres of surrounding waters, an area that, according to surveys, could be exploited for offshore oil.

In 2001, the then Thai government of Thaksin Shinawatra, who was on good terms with Cambodian leader Hun Sen, attempted to settle the issue through an agreement, the Memorandum of Understanding 44, which envisioned joint exploitation of the oil fields, but it remained a dead letter.

Nationalist circles in Thailand are now increasingly pressing for its cancellation, hence, Phnom Penh's move. Fully aware that its naval forces cannot compete with the Thai navy, Cambodia is trying to play the UNCLOS card to safeguard what it believes to be its rights.

The affair has another important aspect, namely the issue of exclusive economic zones, a hot issue in the nearby South China Sea, due to China's unilateral stance in enforcing its own maritime border, the “nine-dash line”.

This is at the heart of the dispute between China and the Philippines and has recently seen numerous shows of force at sea.

Beijing also claims islands, atolls, and offshore areas within the exclusive economic zones of Vietnam, Malaysia, and Brunei (as well as the "rebel island" of Taiwan).

These countries had appealed to UNCLOS for arbitration, which came in 2016 when Beijing’s “nine-dash line” was ruled to have no legal basis.

Yet, despite ratifying UNCLOS in 1996 and reaffirming recently its support for multilateralism, the People's Republic of China has never recognised this ruling and continues to operate within what it believes to be its own maritime borders.

Up to now, within ASEAN, Cambodia had played off Beijing, using its failure to ratify UNCLOS to block any joint position regarding the 2016 arbitration.

Now, just as the Philippines chairs the body that brings together Southeast Asian countries, it will be harder for Phnom Penh to renege on any act by a body it intends to appeal to in order to resolve its dispute with Thailand.

• cambodia
• thailand
• china
• asean
• unclos
• nine-dash line
• border disputes
• south china sea