Biden says US commitments to defend Philippines, Japan 'ironclad' as tensions with China rise

US commitments to defend Japan and the Philippines are "ironclad," President Joe Biden said Thursday as he hosted his regional counterparts amid increasing provocations from China.

"I want to be clear. The United States’ defence commitments to Japan and to the Philippines are ironclad. They are ironclad," the president said during brief remarks to reporters before a first-of-its-kind trilateral summit.

"Any attack on Philippine aircraft, vessels or armed forces in the South China Sea would invoke our mutual defence treaty," he added.

Biden's reassurances came as he hosted Philippine President Ferdinand Marcos Jr. and Japanese Prime Minister Fumio Kishida.

Chinese ships have grown increasingly assertive in the South China Sea, where they have repeatedly antagonised Philippine naval vessels amid conflicting maritime claims.

Marcos has vowed to respond to the incidents, which have included firing upon Philippine Coast Guard ships with water cannons and shining lasers at the vessels.

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"Over the succeeding weeks, there shall be implemented by the relevant national government agencies and instrumentalities a response and countermeasure package that is proportionate, deliberate and reasonable in the face of the open, unabating and illegal, coercive, aggressive and dangerous attacks by agents of the China Coast Guard and the Chinese Maritime Militia," Marcos said on X.

The Chinese Coast Guard has repeatedly tried to block Manila’s supplies to its grounded warship BRP Sierra Madre in disputed waters in the vast waterway. Manila has said the incidents have injured its personnel and damaged its vessels.

China and the Philippines have conflicting claims over the Second Thomas Shoal – also known as the Ayungin Shoal, Bai Co May and Ren'ai Jiao – which is a submerged reef in the Spratly Islands in the South China Sea.

An international tribunal overwhelmingly ruled in favour of the Philippines’ maritime claims in 2016, rejecting much of China's claims, including its efforts to develop artificial islands to stake out naval claims in the South China Sea. Beijing has not recognised the ruling, declaring it "null and void."

The US and the Philippines signed a mutual defence treaty in 1951, just nine years before Washington and Tokyo signed a similar pact.

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A readout of Biden and Marcos' meeting provided by the White House said the leaders "underscored their commitment to international law in the South China Sea” and said Biden reinforced Washington's defence commitment, which it said, "extends to armed attacks on Philippine armed forces, public vessels or aircraft—to include those of its Coast Guard— in the Pacific, including anywhere in the South China Sea."

China has grown increasingly assertive in the Indo-Pacific in recent years as the US under successive administrations has sought to bolster its regional alliances in a bid to push back on Beijing.

Biden hosted Kishida for an official state visit Wednesday followed by a resplendent dinner at the White House replete with pomp and ceremony.

A joint leader statement released by the White House following the conclusion of Thursday's historic trilateral summit said Biden, Kishida and Marcos emphasised their nations' "unwavering commitment to freedom of navigation and overflight and the importance of respecting the sovereign rights of states within their exclusive economic zones consistent with international law, as reflected in the 1982 United Nations Convention on the Law of the Sea."

"We express our serious concerns about the People’s Republic of China’s (PRC) dangerous and aggressive behaviour in the South China Sea. We are also concerned by the militarization of reclaimed features and unlawful maritime claims in the South China Sea," the leaders said.

"We steadfastly oppose the dangerous and coercive use of Coast Guard and maritime militia vessels in the South China Sea, as well as efforts to disrupt other countries’ offshore resource exploitation," they added.