Secretary of State Mike Pompeo said Monday the United States would treat Beijing's pursuit of resources in the dispute-rife South China Sea as illegal, ramping up support for Southeast Asian nations and triggering a furious response from Beijing.
It was the latest forceful statement by President Donald Trump's administration to challenge China, which he has increasingly cast as an enemy ahead of November elections.
"We are making clear: Beijing's claims to offshore resources across most of the South China Sea are completely unlawful, as is its campaign of bullying to control them," Pompeo said in a statement.
"The world will not allow Beijing to treat the South China Sea as its maritime empire."
The United States has long rejected Beijing's sweeping claims in the South China Sea, which is both home to valuable oil and gas deposits and a vital waterway for the world's commerce.
Pompeo's statement goes further by explicitly siding with Southeast Asian nations including the Philippines and Vietnam, after years of the US saying it took no position on individual claims.
"America stands with our Southeast Asian allies and partners in protecting their sovereign rights to offshore resources, consistent with their rights and obligations under international law," Pompeo said.
"We stand with the international community in defense of freedom of the seas and respect for sovereignty and reject any push to impose 'might makes right' in the South China Sea or the wider region."
- Rejecting basis of claims -
Beijing claims most of the South China Sea through a so-called nine-dash line, a vague delineation based on maps from the 1940s.
It has spent years building military bases on artificial islands in the contested areas to cement its claims, while dragging out a diplomatic process to resolve the disputes for nearly two decades.
China on Tuesday responded forcefully to Pompeo's comments, saying the accusation of unlawfulness was "completely unjustified".
"We advise the US side to earnestly honor its commitment of not taking sides on the issue of territorial sovereignty, respect regional countries' efforts for a peaceful and stable South China Sea and stop its attempts to disrupt and sabotage regional peace and stability," said the US embassy in Washington.
The statement accused the United States of trying to "sow discord" between China and its fellow claimants in the sea.
Pompeo issued his statement to mark the fourth anniversary of a tribunal decision that sided with the Philippines against the nine-dash line.
Pompeo said that China, based on the court decision, cannot make claims based on the Scarborough Reef or Spratly Islands, a vast uninhabited archipelago.
The United States as a result now rejects Beijing's claims in the waters surrounding Vanguard Bank off Vietnam, Lucania Shoals off Malaysia, waters considered in Brunei's exclusive economic zone and Natuna Besar off Indonesia, Pompeo said.
"Any PRC action to harass other states' fishing or hydrocarbon development in these waters -- or to carry out such activities unilaterally -- is unlawful," Pompeo said.
Pompeo also rejected Beijing's southernmost claim of Malaysian-administered James Shoal, which is 1,800 kilometers (1,150 miles) from the Chinese mainland.
The 2016 decision was issued by a tribunal under the UN Convention on the Law of the Sea. Pompeo noted that China is a party to it and called the ruling legally binding.
The United States, however, is one of the few countries that is not part of the convention, with conservatives opposing any loss of autonomy to a global body.
- Friction across fronts -
The South China Sea statement comes amid rising tensions surrounding China, including a deadly border clash last month with India that Pompeo called part of a strategy by Beijing to challenge its neighbors.
Trump has also strongly criticized China for not doing more to stop the coronavirus pandemic, news of which was initially suppressed when it emerged in Wuhan late last year.
Critics both at home and abroad say that Trump is hoping to deflect attention ahead of the November election over his handling of the virus in the US, which has suffered by far the highest death toll of any country.
Trump, after bipartisan calls in Congress, has also stepped up pressure on China over its incarceration of more than one million Uighurs and other Turkic Muslims.
The United States last week imposed sanctions on Chinese officials over Xinjiang, leading to a reciprocal effort by Bejiing against senior American lawmakers.