WASHINGTON--President Joe Biden said Thursday that U.S. defense commitment to Pacific allies was “ironclad” as he gathered Philippine President Ferdinand Marcos Jr. and Japanese Prime Minister Fumio Kishida at the White House on Thursday in the midst of growing concern about provocative Chinese military action in the Indo-Pacific.

The U.S. and the Philippines have had a mutual treaty in place for more than 70 years. Biden's forceful reinforcement of the American commitment comes in the midst of persistent skirmishes between the Philippine and Chinese coast guards in the disputed South China Sea.

“The United States defense commitments to Japan and to the Philippines are ironclad. They’re ironclad," Biden said as he began three-way talks at the White House with Kishida and Marcos. "As I said before, any attack on Philippine aircraft, vessels or armed forces in the South China Sea would invoke our mutual defense treaty.”

Relations between China and the Philippines have been repeatedly tested by skirmishes involving the two nations’ coast guard vessels in the disputed South China Sea. Chinese coast guard ships also regularly approach disputed Japanese-controlled East China Sea islands near Taiwan.

The so-called “gray-zone” harassment by China has included shining military-grade lasers at the Philippine Coast Guard, firing water cannons at vessels and ramming into Philippine ships near the Second Thomas Shoal, which both Manila and Beijing claim. In 1999, Manila intentionally ran the World War II–era ship aground on the shoal, establishing a permanent military presence there.

Biden, in a wide-ranging phone call with Chinese President Xi Jinping last week, raised concerns about China’s operations in the South China Sea, including efforts to impede the Philippines, which the U.S. is treaty-obligated to defend, from resupplying its forces on the Second Thomas Shoal.

Chinese officials have bristled at criticism over their action in the South China Sea and blamed the U.S. for exacerbating tensions.

“No one should violate China’s territorial sovereignty and maritime rights and interests, and China remains steadfast in safeguarding our lawful rights,” Chinese Foreign Ministry spokeswoman Mao Ning said Thursday.

The White House billed the first-ever trilateral summit with Japan and the Philippines as a potent response to China’s attempts at “intimidation” and sending a message that China is “the outlier in the neighborhood,” according to an administration official.

The leaders are also expected to announce that their coast guards will hold a joint patrol in the Indo-Pacific this year, a follow-up on law enforcement drills carried out last year by the allies in waters near the disputed South China Sea. The U.S. Coast Guard will also welcome Filipino and Japanese coast guard members onto a U.S. Coast Guard vessel during the patrol for training, according to senior Biden administration officials who insisted on anonymity to preview the talks.

The summit comes a day after Biden held one-on-one talks with Kishida and feted the Japanese premier with a glitzy state dinner at the White House, a diplomatic honor meant to recognize Tokyo's growing clout on the global stage. It was also designed to send a clear signal that the Democratic administration remains determined to build what it calls a “latticework” of alliances in the Indo-Pacific even as it grapples with the Israel-Hamas war and Russia's ongoing invasion of Ukraine. Biden also hosted Marcos for a private meeting at the White House ahead of the scheduled three-way talks.

"Today’s summit is an opportunity to define the future that we want, and how we intend to achieve it together," Marcos said.

Thursday's three-way summit will also have a large economic component with several major U.S.-based companies — including Meta, UPS and Greenbrier Energy — announcing investments in the Philippines, administration officials said. The new deals come after Commerce Secretary Gina Raimondo visited Manila last month to announce more than $1 billion in new investment by American companies in the Philippines.

Biden also announced that the three nations were launching a a new economic corridor in the Philippines as part of the G7 Partnership for Global Infrastructure Investment that would help develop clean energy, port, agriculture and other projects in the country. Biden said the leaders were forging a “new era” and predicted “a great deal of history in our world will be written in the Indo-Pacific in the coming years.”

The United States, the United Kingdom and Japan on Wednesday announced joint military exercises in the Indo-Pacific in 2025. That followed the Pentagon revealing earlier this week that the U.S., the U.K. and Australia were considering including Japan in the AUKUS partnership, a grouping launched in 2021 that aims to equip Australia with nuclear-powered and conventionally armed submarines.

Kishida visited Capitol Hill on Thursday for an address to U.S. lawmakers that focused on the need to strengthen the partnership between the U.S. and Japan at a time of tension in the Asia-Pacific and skepticism in Congress about U.S. involvement abroad. He offered concern about “the undercurrent of self-doubt among some Americans about what your role in the world should be.”

Biden has made improving relations with the Philippines a priority since Marcos became the country's president in June 2022. The relationship has had ups and downs over the years and was in a difficult place when Marcos took office. Human rights groups said Marcos’ predecessor, Rodrigo Duterte's “war on drugs” resulted in thousands of extrajudicial killings.

Marcos, the son and namesake of the country’s former dictator, as a candidate said he would look to pursue closer ties with China. But he's increasingly drifted toward Washington amid concerns about China’s coercive action.

Biden hosted him for talks at the White House last year, the first Washington visit by a Philippine president in more than a decade. Biden also met him on the sidelines of the U.N. General Assembly soon after Marcos took office, and dispatched Vice President Kamala Harris to Manila in 2022 to meet him.

Last year, the Philippines agreed to give the U.S. access to four more bases on the islands.