The US administration has upheld a Trump-era rejection of nearly all of China’s significant maritime claims in the South China Sea.
Joe Biden’s government also warned China that any attack on the Philippines in the flashpoint region would draw a US response under the terms of a mutual defence treaty.
The stern message from US secretary of state Antony Blinken came in a statement released ahead of this week’s fifth anniversary of an international tribunal’s ruling in favour of the Philippines, against China’s maritime claims around the Spratly Islands and neighbouring reefs and shoals.
China rejects the ruling.
Ahead of the fourth anniversary of the ruling last year, Donald Trump’s administration also said it regarded virtually all Chinese maritime claims in the South China Sea outside China’s internationally recognised waters as illegitimate.
Sunday’s statement reaffirms that position, which had been laid out by Mr Trump’s secretary of state, Mike Pompeo.
“Nowhere is the rules-based maritime order under greater threat than in the South China Sea,” Mr Blinken said, using language similar Mr Pompeo.
He accused China of continuing “to coerce and intimidate south-east Asian coastal states, threatening freedom of navigation in this critical global throughway”.
“The United States reaffirms its July 13 2020 policy regarding maritime claims in the South China Sea,” he added, referring to Mr Pompeo’s original statement.
“We also reaffirm that an armed attack on Philippine armed forces, public vessels, or aircraft in the South China Sea would invoke US mutual defence commitments.”
Article IV of the 1951 US-Philippines Mutual Defence Treaty obligates both countries to come to each other’s aid in case of an attack.
Prior to Mr Pompeo’s statement, US policy had been to insist that maritime disputes between China and its smaller neighbours be resolved peacefully through UN-backed arbitration.
The shift did not apply to disputes over land features that are above sea level, which are considered to be “territorial” in nature.
Although the US continues to remain neutral in territorial disputes, it has effectively sided with the Philippines, Brunei, Indonesia, Malaysia and Vietnam, all of which oppose Chinese assertions of sovereignty over maritime areas surrounding contested South China Sea islands, reefs and shoals.
China reacted angrily to the Trump administration’s announcement and is likely to be similarly peeved by the Biden administration’s decision to retain and reinforce it.
“We call on (China) to abide by its obligations under international law, cease its provocative behaviour, and take steps to reassure the international community that it is committed to the rules-based maritime order that respects the rights of all countries, big and small,” Mr Blinken said in the statement.
China has rejected the tribunal’s decision, which it has dismissed as a “sham”, and has refused to participate in arbitration proceedings.
It has continued to defy the decision with aggressive actions that have brought it into territorial spats with Vietnam, the Philippines and Malaysia in recent years.
As with last year’s statement, Sunday’s announcement came amid heightened tensions between the US and China over numerous issues, including the coronavirus pandemic, human rights, Chinese policy in Hong Kong and Tibet and trade, which have sent relations plummeting.
China claims almost all of the South China Sea and routinely objects to any action by the US military in the region.
Five other governments claim all or part of the sea, through which approximately five trillion dollars (£3.5 trillion) in goods are shipped every year.
China has sought to shore up its claims to the sea by building military bases on coral atolls, leading the US to sail its warships through the region on what it calls freedom of operation missions.
The United States has no claims itself to the waters but has deployed warships and aircraft for decades to patrol and promote freedom of navigation and overflight in the busy waterway.