Philippine Foreign Secretary Teddy Locsin, left, shakes hands with visiting Secretary of State Mike Pompeo after their joint news conference in Manila. (Ted Aljibe/AFP/Getty Images)

Secretary of State Mike Pompeo said Friday that any attack on Philippine aircraft or ships in the South China Sea would trigger a response from the United States under a mutual defense treaty between the two countries, a firm assurance to its longtime ally amid rising Chinese militarization in the contested waters. 

Pompeo’s comments seek to reassure the Southeast Asian country at a time when China is building military outposts on artificial islands it has claimed for its own in the South China Sea. China says it has historic rights to the crucial waterway, where one-third of global trade flows, but its claims overlap with those of several other nations in the region, including Vietnam and the Philippines. 

“China’s island building and military activities in the South China Sea threaten [Philippine] sovereignty, security and therefore economic livelihood, as well as that of the United States,” Pompeo said at a joint news conference in Manila, where he landed Thursday night after the Hanoi summit between President Trump and North Korean leader Kim Jong Un.

“As the South China Sea is part of the Pacific, any armed attack on Philippine forces, aircraft or public vessels in the South China Sea will trigger mutual defense obligations under Article 4 of our mutual defense treaty,” Pompeo added. 

The article spells out that the Philippines and the United States would come to each other’s defense if either were attacked, as such an attack on either party would “be dangerous to its own peace and safety.”

Pompeo’s visit also comes at a time when the long-standing alliance between the Philippines and the United States is being questioned by some skeptics inside the administration of Philippine President Rodrigo Duterte, who has been courting investment from and closer ties with China. In November, President Xi Jinping visited Manila, becoming the first Chinese leader to make a state visit here in more than a decade.

Pompeo, who is making his first trip to Manila as secretary of state, met with Duterte as well as Philippine Foreign Secretary Teddy Locsin.

A pro-China camp in the Duterte administration “is using the argument that China is a geographical reality, whereas America is a geopolitical anomaly,” said Richard Heydarian, a Manila-based defense and security analyst. “People are asking: ‘Do we really need America? That’s so Cold War.’ ”

Philippine Defense Secretary Delfin Lorenzana has called for a review of the 1951 Mutual Defense Treaty between Washington and Manila, the agreement that guarantees a U.S. military response if the Philippines is attacked. The Philippine defense establishment has long argued that the language of the document is too vague, especially as China gets more aggressive in the waters off the Philippine archipelago.

A report last month from the Asia Maritime Transparency Initiative (AMTI), run by the Center for Strategic and International Studies, said China sent a large fleet of almost 100 ships to stop construction work by the Philippines on an island in the disputed Spratly chain. 

After Pompeo’s assurances that the South China Sea is covered in the mutual defense agreement, the “impetus will be on Manila to decide whether that’s good enough,” said Greg Poling, director of the AMTI.

At their joint news conference Friday, Locsin said the review of the mutual defense treaty was something that “requires further thought,” indicating he believed that Pompeo’s comments were a sufficient guarantee.

“We are very assured, we’re very confident, that the United States has — in the words of Trump to our president: We have your back,” he said.

Speaking to reporters as he flew to Manila from Hanoi, Pompeo said he was “absolutely” concerned about Chinese influence in the Philippines and more broadly across the region. In his Friday statement, he warned his counterparts about Chinese state-backed companies, which have promised billions of dollars in big-ticket infrastructure and investment in the Philippines under Duterte.

“American companies . . . operate with the highest standards of transparency and adherence to the rule of law,” said Pompeo. “The same cannot be said for Chinese state-run or state-backed enterprises.”

Mahtani reported from Hong Kong.