|The Fiery Cross Reef in the Spratly archipelago is illegally developed by China into an artificial island. (Photo: Getty)
"International law does not recognize sovereignty acquired through conquest," Thayer said by e-mail.
Beijing's move also violates the Declaration on Conduct of Parties in the South China Sea (DOC) that was agreed to by China and ASEAN members in 2002.
Thayer pointed out Paragraph 5 of the DOC, which states that "The Parties undertake to exercise self-restraint in the conduct of activities that would complicate or escalate disputes and affect peace and stability" in the South China Sea.
"China’s unilateral action seriously complicates the dispute and affects peace and stability in the South China Sea," Thayer said. "Chinese administrators will issue regulations and directives that seriously affect the sovereignty and sovereign jurisdiction of both Vietnam and the Philippines," he noted.
Meanwhile, former Philippine Foreign Secretary Albert Del Rosario on April 19 urged the Philippine government to protest China's establishment of two districts aimed at exerting control over the East Sea, where the Philippines and other Asian nations have overlapping claims.
"We therefore respectfully urge our government to protest this recent action of China, as it rightly did over the sinking of the Vietnamese fishing boat on April 8, 2020," Del Rosario said in a statement.
He also accused China of exploiting the new coronavirus pandemic to advance its "illegal" claims in the waters.
"These recent events in the South China Sea remind us Filipinos to be eternally vigilant in the defense of our country’s territory and sovereign rights even as we confront a very grave threat as COVID-19," he said.
"These show that China has been relentless in exploiting the COCID-19 pandemic as it continues to pursue its illegal and expansive claims in the South China Sea to the prejudice of Filipinos, the ASEAN States and the international community as a whole," Del Rosario said.
He also warned that China’s declaration of a new administrative district in the Spratlys "is a pre-emptive move to push aside sovereignty claims by Vietnam and the Philippines."
The South China Morning Post earlier reported that the two new districts will be under the authority of the local government in Sansha, a city in the southern island of Hainan.
These new districts, the report added, "will govern the Paracels and Macclesfield Bank—an area claimed by Vietnam and Taiwan—as well as the Spratly Islands and their adjacent waters, where there are multiple overlapping claims."
In response to China’s move, Vietnamese Foreign Ministry spokesperson Le Thi Thu Hang on April 19 voiced Vietnam’s strong objection to China’s establishment of the so-called “Sansha city” and related acts as they seriously violated Vietnam’s sovereignty.
“Vietnam has strongly affirmed many times that it has sufficient historical evidence and legal foundation to assert its sovereignty over the Hoang Sa and Truong Sa archipelagos,” the official said.
She emphasized that those moves of China are null and void, unrecognized, and they give no benefits to the friendship among nations and further complicate the situation in the East Sea, the region and the world.
“Vietnam demands that China respect Vietnam’s sovereignty, abrogate its wrongful decisions regarding the moves and not to take similar acts in the future,” Hang added.