The People’s Republic of China (PRC) urged the US on Thursday to halt passage of military ships in the Taiwan Strait. A spokesperson for the PRC Ministry of National Defense stated that the US must “stop abusing international law,” and  “cease all dangerous provocations.” The statement was in response to the recent passage of a US naval destroyer through the politically sensitive area.

The PRC claims the Taiwan Strait as internal waters under the United Nations Convention on the Law of the Sea (UNCLOS). As such, PRC claims to exercise full sovereignty over its internal waters as if they were part of its land territory. Full sovereignty includes the right to govern access to the area.

PRC’s claim to the straight as internal stems from the country’s One China Policy. The PRC Constitution’s preamble states Taiwan is part of their national territory and “[i]t is the sacred duty of all the Chinese people… to achieve the great reunification of the motherland.” However, Taiwan asserts an overlapping claim to the straight. Article 4 of Taiwan’s Constitution claims all territory “according to its existing national boundaries.” The article does not expressly state what territory is included in “national boundaries.” Despite the lack of clarity, the long-standing view has been that Taiwan claims all PRC territory. It is unclear whether either claim would allow the Taiwan Strait to be classified as internal waters, per the language of UNCLOS.

The statement from the PRC was issued at a time of escalating tensions between the two countries. Taiwan’s recent elections saw Lai Ching-te, the country’s Vice President, elected to lead the country. Ching-te was seen as unfavorable by the PRC due to his close relations with the US. The US is Taiwan’s closest ally. The Taiwan Relations Act stipulates that the US will assist in the defense of the country. US President Joe Biden said in a CBS 60 Minutes interview last year that the US was committed to the agreement.

The PRC is currently involved in numerous territorial disputes over the control of surrounding bodies of water. Tensions over claims in the South China Sea resulted in the Philippines filing a case with the Permanent Court of Arbitration (PCA) in the Hague. The court found largely for the Philippines. However, the PRC rejected the ruling.