Washington (CNN) — The United States’ commitments to the defense of Japan and the Philippines remain “ironclad,” President Joe Biden said on Thursday as he hosted the leaders of those countries amid their separate territorial disputes with China.

The comments came as Biden hosted the first ever trilateral summit between the three countries, welcoming Filipino President Ferdinand Marcos Jr. to the White House a day after the official visit of Japanese Prime Minister Fumio Kishida.

“When we stand as one, we’re able to forge a better future for all,” Biden said in the East Room of the White House Thursday.

Japan and the Philippines both have separate territorial disputes with China, in the former’s case the Senkaku Islands in the East China Sea and in the latter’s areas of the South China Sea.

Philippines-China tensions have focused on Second Thomas Shoal, which sits about 200 kilometers (125 miles) from the coast of the Philippine island of Palawan. In the 1990s, the Philippines grounded an aging World War II-era navy transport ship on the shoal, to help enforce its claim to the area. The ship is now mostly a rusted wreckage and is manned by Filipino marines stationed on rotation.

Meanwhile, China claims the shoal, which is in the Philippines’ exclusive economic zone, as its sovereign territory, as it does much of the South China Sea, in defiance of an international arbitration ruling. Recent clashes have occurred when Philippine attempts to resupply the forces on the ship have been met by China Coast Guard ships firing water cannons at the Philippine resupply boats, resulting in injuries to Filipino sailors and damage to the vessels.

Referencing the Filipino-Chinese tensions, Biden on Thursday said “any attack on Philippine aircraft, vessels or armed forces in the South China Sea would invoke our mutual defense treaty.”

The 1951 mutual defense treaty between the US and the Philippines – the oldest such US pact in the Asia-Pacific – stipulates both sides would help defend each other if either were attacked by a third party.

Thursday’s meeting marks the latest attempt by the administration to grapple with that sort of Chinese aggression, and a senior administration official said ahead of the meeting that the White House is very concerned by China’s actions in the South China Sea.

“What you’ll see is a clear demonstration of support and resolve from both President Biden and Prime Minister Kishida that we stand shoulder to shoulder with Marcos ready to support and work with the Philippines at every turn,” one official said ahead of Thursday’s meeting.

Marcos said on Thursday that the Philippines, Japan and the United States “meet today as friends and partners bound by a shared vision in pursuit of a peaceful, stable and prosperous Indo-Pacific.”

The three countries, Marcos added, are “linked by a profound respect for democracy, good governance and the rule of law.”

The meeting comes as the region is grappling with the uncertainty of China’s aggressive posture toward Taiwan and the South China Sea along with nuclear provocations from North Korea and its burgeoning relationship with Russia – concerns that have drawn regional allies closer to the US.

Japan has been at the center of Biden’s alliance building in the Indo-Pacific as officials have seen a willing partner in Kishida, who has significantly shifted the country’s defense posture in recent years and provided ongoing support to Ukraine amid Russia’s invasion of Ukraine. Kishida has committed to increasing defense spending by 2% of GDP by 2037 and acquired American Tomahawk missiles to increase its counterstrike capabilities.

Biden hosted Marcos at the White House last year, showing his intent to reestablish strong ties with Manila that had frayed under former President Rodrigo Duterte, who sought closer relations with China.

“We’re going to continue to support the Philippines military’s modernization goals,” Biden told the visiting leader during that visit, pledging the two nations “not only share a strong partnership – we share a deep friendship, one that has been enriched by millions of Filipino Americans in the communities all across the United States.”

A highlight of Thursday’s meeting were several announcements meant to bolster the Philippines amid those clashes.

A senior administration official also said that on Thursday the White House will be announcing a new infrastructure project in the Philippines. CNN reported earlier this week one of the announcements will be the development of a new rail and shipping corridor between Philippines’s Clark Air Base and Subic Naval Base, a move that’s meant to send a clear message to Beijing.

Biden briefly referenced that economic corridor on Thursday: “It means more jobs for people across the entire region,” he said. “It means more investment in sectors critical to our future – clean energy, ports, railroads, agriculture and much more.”

The White House is also expected to increase the Filipino military’s capability with a new infrastructure investment similar to what the US announced in India in the leadup to the G20.

In the days leading up to the summit, the US, Japan and Philippines – along with Australia – conducted maritime military exercises near Philippines’ Exclusive Economic Zone (EEZ), after Philippine vessels had alleged “harassment” by Chinese ships in the South China Sea.

The senior official added that the White House will also be making announcements in “Open Radio Access Network technology” and that both the US and Japan will be providing millions of dollars in funding.

Officials also said they will announce an upcoming Coast Guard patrol in the Indo-Pacific that will be taking place “in the coming year.”

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