Prime Minister Fumio Kishida of Japan said on Friday that his country would start formal talks with the Philippines to allow the deployment of Japanese troops to the Southeast Asian country, further strengthening ties between two countries that have embraced each other as bulwarks against China.
“We share serious concerns on the situation in the East China Sea and South China Sea,” Mr. Kishida said, referring to Beijing’s increasingly assertive actions in the region. “The attempt to unilaterally change the status quo by force is unacceptable.”
Mr. Kishida’s announcement came after a meeting with President Ferdinand Marcos Jr. of the Philippines, at the beginning of a two-day visit to Manila. It was Mr. Kishida’s first trip to the country since he took office in 2021.
The countries are locked in territorial disputes with Beijing — the Philippines in the South China Sea and Japan in the East China Sea — and they flank Taiwan, the self-governed island that China has vowed to reclaim by force.
The proposed pact, known as a reciprocal access agreement, would give the Japanese military access to bases in the Philippines and make it easier to conduct more joint drills.
The two countries began exploring the idea for such an agreement in 2015, but the issue has taken on greater urgency as they have found themselves increasingly confronted by a more assertive China, with Mr. Marcos saying the pact would help maintain “peace and stability in our region.”
Japan plans to give coastal radar systems worth about $4 million to improve the Philippine Navy’s capabilities as part of its official security assistance program, Mr. Kishida said.
Japan announced in April that the Philippines would be one of the main recipients of the aid program and has provided Manila with coast guard vessels, satellite communications systems, and air surveillance radars.
The two countries have relations that go back at least six decades. Japan is the biggest backer of infrastructure projects in the Philippines, providing aid for projects such as the subway in Manila, as well as bridges and railways around the country.
Military ties took off in 2012, after Shinzo Abe took office as the Japanese prime minister, and continued even under President Rodrigo Duterte of the Philippines.
Much of the deepening engagement also involves the United States, a treaty ally of both the Philippines and Japan. The three countries have participated in large-scale military exercises and conducted drills in the South China Sea since the beginning of the year. On Friday, both Mr. Kishida and Mr. Marcos said they wanted to strengthen the trilateral cooperation.
Mr. Marcos, who took office in June 2022, succeeding Mr. Duterte, has adopted a muscular foreign policy approach, seeking alliances and restoring the Philippines’ military ties to the United States and others to counter China.
In the Philippines, there is broad popular support for Japan’s involvement, despite its brutal occupation during World War II. Dindo Manhit, the president of Stratbase ADR, a research organization based in Manila, said the group’s surveys showed that Japan was the most trusted country in the Philippines, after the United States.
“Every time the U.S. suddenly blows hot and cold, Japan has been consistent,” he said.
Beijing claims 90 percent of the South China Sea, some of it hundreds of miles from the Chinese mainland, in waters surrounding Vietnam, Malaysia, Brunei, Indonesia, and the Philippines.
In the past decade or so, China has asserted greater control over the region, using the Paracel and the Spratly island chains to expand its reach by building and fortifying outposts and airstrips.
That has alarmed much of Asia and the United States, which says it has a vested interest in maintaining freedom of navigation in one of the world’s busiest shipping lanes. China’s military buildup and increasingly aggressive maritime actions have raised questions about its intentions in the region and its willingness to comply with international law and norms. Beijing says its actions are in accordance with the law because it has “indisputable sovereignty” over these islands in the South China Sea.
Those concerns are felt perhaps most acutely in the Philippines, where fishermen have been blocked by Chinese vessels and Manila has been prevented from fully exploring oil and gas deposits within an area that an international tribunal ruled to be part of its exclusive economic zone.
Tensions have recently escalated between the Philippines and China in the disputed waters. Last month, Chinese ships collided with a Philippine coast guard vessel and a supply boat in the South China Sea, prompting condemnations from countries including Japan and the United States, which reiterated that it would come to the aid of the Philippines if it came under armed attack.
On Saturday, Mr. Kishida is set to address a joint session of the Philippine congress. He will be the first Japanese prime minister to do so.