“The US stands with our Philippine ally in rejecting China’s destabilising plans to establish a ‘national nature reserve’ at Scarborough Reef,” Rubio wrote on the X social media platform on Friday.

“This is yet another coercive attempt to advance China’s interests at the expense of its neighbours and regional stability,” Rubio said.

“… Claiming Scarborough Reef as a nature preserve is another example of Beijing using pressure tactics to push expansive maritime and territorial claims, disregarding the rights of neighbouring countries,” he added in a statement.

On Wednesday, China’s State Council revealed its intention to establish a nature reserve spanning 3,500 hectares (8,650 acres) on the disputed islet, describing the initiative as an “important guarantee for maintaining … diversity, stability and sustainability”.

While Scarborough Shoal lies 240km (150 miles) west of the Philippines’ main island of Luzon and is included in the country’s exclusive economic zone, it has been under Beijing’s control since 2012.

China’s nature reserve plans drew a string of strong responses from the Philippines, where the Department of Foreign Affairs promised on Thursday to lodge a “formal diplomatic protest against this illegitimate and unlawful action”.

According to the Philippine Star news outlet, Philippine National Security Adviser Eduardo Ano said China’s planned “Huangyan Island National Nature Reserve” is “patently illegal”.

Ano cited violations of the United Nations Convention on the Law of the Sea (UNCLOS), the 2016 arbitral ruling in favour of Manila regarding China’s claims in the sea, and the 2002 Declaration on the Conduct of Parties in the South China Sea.

“This move by the People’s Republic of China is less about protecting the environment and more about justifying its control over a maritime feature that is part of the territory of the Philippines and its waters lie within the exclusive economic zone of the Philippines,” Ano was quoted in the newspaper.