MANILA, Philippines (AP) -- Taiwan's foreign minister has flown to the Philippines as head of a high-level delegation of investors, two senior Philippine officials said Saturday, prompting a protest from China and a warning to Manila "not to play with fire."

Relations between China and the Philippines have been strained as their coast guards and other forces spar in increasingly tense confrontations over the ownership of islands and fishing grounds in the disputed South China Sea. Taiwanese Foreign Minister Lin Chia-lung's visit earlier this week to Manila and the Clark Freeport Zone, an industrial hub north of the capital, has exacerbated the tensions.

Philippine officials have publicly neither confirmed nor denied news reports of Lin's visit, but two members of President Ferdinand Marcos Jr.'s Cabinet told The Associated Press that Taiwan's top diplomat flew to the country "in his private capacity" to lead a major delegation of Taiwanese investors and business executives in the semiconductor and other key industries.

Lin did not have any official engagements with political and security officials while in the Philippines for two or three days, said the two officials, who did not elaborate and spoke on condition of anonymity because they were not authorized to discuss the matter publicly.

Under a "One China" policy, the Philippines does not recognize Taiwan as a sovereign state. China claims Taiwan as part of its territory, which could be annexed by force if necessary, and opposes the self-governing island having official interactions with other countries, particularly the United States.

The Department of Foreign Affairs in Manila said Friday that the Philippines has "consistently upheld" that policy, which is "clear and unwavering." It added, however, that "the Philippines maintains economic and people-to-people engagements with Taiwan, particularly in the areas of trade, investment, and tourism. These interactions are conducted within the bounds of our One China Policy."

The department said that "no official from Taiwan (was) recognized as a member of the business delegation that recently visited the Philippines," suggesting that Lin came as a private business representative.

The Ministry of Foreign Affairs in Beijing issued a strongly worded protest in Manila and Beijing and said that by allowing Lin to visit, the Philippines has provided a platform for "'Taiwan independence' separatists to engage in anti-China activities" and has "severely violated its own commitment on Taiwan-related issues."

It urged the Philippines to "stop pursuing the wrong course and return to the right track at once, stop playing with fire on issues concerning China's core interests." It warned the Philippines not to "underestimate the firm resolve of the Chinese people to safeguard our sovereignty and territorial integrity."

"There is a price to pay for trampling on China's red line, and all consequences arising therefrom will be borne by the Philippines," the Chinese foreign ministry said.