Harris is the highest-ranking US official to visit Manila since President Ferdinand Marcos took power in June, signaling a growing rapport between the long-time allies after years of frosty relations under his Beijing-friendly predecessor Rodrigo Duterte.

She also met with her Philippine counterpart Sara Duterte, the daughter of the former leader whose deadly drug war sparked an international investigation into alleged human rights abuses.

"We stand with you in defense of international rules and norms as it relates to the South China Sea," Harris told Marcos at the start of talks in the presidential palace in Manila.

"An attack on the Philippine armed forces, public vessels or aircraft in the South China Sea would invoke the US mutual defense commitment [...] that is our unwavering commitment to the Philippines."

Marcos said he did not "see a future for the Philippines that does not include the United States."

The US has a long and complex relationship with the Philippines -- and the Marcos family. Marcos's dictator father ruled the former US colony for two decades with the support of Washington, which saw him as a Cold War ally.

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