The Thai Navy has seized a Cambodian fishing boat and arrested its crew after they were allegedly found to have entered Thai waters illegally, prompting a protest from Cambodia that the act, in an area that Cambodia claimed as its territory, was illegitimate. The maritime boundary is one of the simmering tensions on the Thai-Cambodian land border.

On Sunday (22 February), the Thai First Naval Area Command reported that a fishing vessel was detected at latitude 11°31.51’ North and longitude 102°53.40’ East. The area is allegedly within Thai waters, approximately 13.4 nautical miles from Khlong Yai District in Trat Province.

The vessel was not registered with any state, but the three crew members were Cambodian nationals with no identification documents. The crew stated that they were hired by a Cambodian employer to fish and claimed that they were unaware that they had entered Thai waters. It was reported that they had been fishing in Thai waters for two days.

All were arrested and detained for legal proceedings. The vessel was taken to the Khlong Yai Multipurpose Port for processing.

Meanwhile, the Cambodian Foreign Ministry issued a statement to formally protest Thailand’s unlawful enforcement of its law within Cambodia’s territorial seas and called for the release of the Cambodian crew members. The statement said that the incident occurred at 7.2 nautical miles from Koh Yor, Koh Kong Province.

“These actions constitute a clear violation of Cambodia’s sovereignty and territorial sea as well as international law,” according to the statement.

Cambodia also called on Thailand to cease all unauthorised naval patrols and law enforcement activities within Cambodia’s territorial seas and take appropriate measures to prevent the recurrence of such actions in the future.

The Thai Navy later insisted that the vessel had intruded into Thai waters, and the crew was detained under a law authorising naval officers to suppress certain maritime offences. According to the coordinates, the vessel had intruded approximately one nautical mile into Thai waters from the Thai-Cambodian maritime boundary.

When being asked about the incident where Cambodia denounced Thailand for its unlawful act on Cambodian territorial sea in his interview on Monday (23 February),Thai Foreign Minister Sihasak Phuangketkeow told France 24 that he did not think that the area belongs to Cambodia's territorial sea, noting that "this is the tactics that the Cambodians have always employed to put pressure on Thailand and to portray Thailand as a more aggressive country." He also added that what Cambodia are doing partly might be for its domestic political purposes.

The incident has heightened mistrust in the already strained relations between the two countries amid the simmering tensions along the Thai-Cambodian land border, which culminated in deadly clashes in July and December 2025.

Thailand and Cambodia share an 817-kilometre border stretching from the Phanom Dong Rak mountain range to the Gulf of Thailand. The border was demarcated under the Franco-Siamese treaties of 1904 and 1907 which Thailand, or Siam at the time, signed with the French colonial authorities when Cambodia was a French protectorate. The demarcation was later seen as incomplete and ambiguous, leading to prolonged conflicts between the two countries.

The two countries later signed an MoU in 2000 on the land border and another in 2001 on the maritime boundary to establish bilateral mechanisms in order to address the issue. However, the maritime boundary between the two countries has yet to be settled.

The tensions in 2025 were centred on the land border, but the conflict has gradually moved to the sea. Amid rising nationalist sentiment, some Thai nationalist groups have called on the government to unilaterally cancel the 2001 MoU with Cambodia on the grounds that these agreements could lead to the loss of territory, particularly Ko Kut.

Meanwhile, the Thai Foreign Ministry insists that the 2001 MoU does not mean that Thailand has accepted the boundary drawn by Cambodia. Rather, it serves as a framework for further negotiations. In particular, it was settled that Ko Kut is unquestionably under Thai sovereignty.

However, Thai PM Anutin Charnvirakul, who has supported the tough stance taken by the Thai military, has repeatedly seemed to play along with the sentiment. He revealed on 10 February that he would consider cancellation of the 2001 MoU.

According to the 2001 MoU, Thailand and Cambodia have an overlapping claims area of 26,000 square kilometres. Around 10,000 square kilometres north of latitude 11° North is still to be delimited, while the remaining area was designated as a Joint Development Area (JDA).

Thai-Cambodian Overlapping Claims Area according to the 2001 MoU

Using the detained vessel’s geographic coordinates provided the Thai Navy, Prachatai found it was located within the disputed, undelimited area. This may explain why both countries claimed that the vessel was within their territorial seas.

Approximate geographic coordinates of the vessel provided by the Thai Navy

Thailand’s claims rely on the 1973 Royal Proclamation establishing the Continental Shelf in the Gulf of Thailand, while Cambodia bases its claims on a domestic law of 1972. These unilateral declarations are binding only on the state that issued them.

While conflicts along the land border have been ongoing, incidents in the Gulf of Thailand could expand the scope of disputes between Thailand and Cambodia, particularly under the Anutin-led government, after it secured victory in the 8 February election.