Marcos has sought to deepen defence cooperation with the United States as he stands up to Chinese actions in the South China Sea, which Beijing claims almost entirely.
"China's determining influence over the security situation and the economic evolution of this region is a permanent fact," Marcos said in a speech at the Shangri-La Dialogue in Singapore, a major security forum attended by defence ministers from around the world.
"At the same time, the stabilising presence of the United States is crucial to regional peace. It's never a choice. Both countries are important."
The Philippines, a treaty ally of the United States, is a key focus of Washington's efforts to strengthen alliances and partnerships in the Asia-Pacific region as it seeks to counter China's growing military might and influence.
Given its position in the South China Sea and proximity to self-ruled Taiwan, which China claims as its own, Philippine support would be crucial for the United States in the event of any conflict.
The Philippines expanded a 2014 agreement last year to give the US military access to another four of its bases, taking the total to nine, including two in the far north of the country less than 450 kilometres (280 miles) from Taiwan.
The Enhanced Defence Cooperation Agreement allows US troops to rotate through and store defence equipment and supplies.
The United States' growing presence in the region and its regular deployment of warships and fighter jets in the Taiwan Strait and South China Sea have infuriated China's leaders in Beijing.
China has accused the United States of using the Philippines as a "pawn to stir up trouble in the South China Sea".
- 'Illegal, coercive, aggressive' -
Manila and Beijing have a long history of maritime territorial disputes, but tensions have worsened under Marcos.
In an effort to win international backing for its stance, Manila has published images of incidents involving Chinese and Philippine vessels and invited local and foreign media on its patrol boats.
China Coast Guard vessels have used water cannon against Philippine boats multiple times in the contested waters, where there have also been collisions that injured several Filipino troops.
"Illegal, coercive, aggressive and deceptive actions continue to violate our sovereignty, sovereign rights and jurisdictions," Marcos said Friday.
"I do not intend to yield," he said. "Filipinos do not yield".
Beijing defends its actions as "legitimate" and "necessary law enforcement measures" in response to Philippine vessels that it says have illegally entered its territorial waters.
"China has never used its size to bully smaller countries, nor would it ever do so, but China has always been principled, and has bottom lines," He Lei, a Chinese general and former vice president of the Academy of Military Sciences, told reporters after Marcos's speech.
"It will never allow certain countries to act outrageously."
China claims almost the entire waterway, brushing off rival claims from other countries, including the Philippines, and ignoring an international ruling that its claims have no legal basis.
To assert its stance, Beijing deploys coast guard and other boats to patrol the waters and has turned several reefs into artificial islands that it has militarised.
Many of the confrontations between Chinese and Philippine vessels have happened near Second Thomas Shoal in the Spratly Islands.
The reef, where a handful of Filipino troops are garrisoned on a grounded navy vessel, is about 200 kilometres (120 miles) from the western Philippine island of Palawan, and more than 1,000 kilometres from China's nearest major landmass, Hainan island.
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