TAIPEI, TAIWAN—Taiwan’s leader said Tuesday the people of the island want to maintain self-rule despite recent electoral gains by the Beijing-friendly opposition party.

Taiwanese officials should not enter into any secret dialogue with China, President Tsai Ing-wen warned in a New Year’s speech.

The opposition Nationalist Party won 15 of 22 major seats in local elections last month, reversing the advantage held by Tsai’s Democratic Progressive Party. She has resigned as party head.

Beijing could woo China-friendly election victors ahead of the next presidential election in 2020. China claims Taiwan as its own territory and has sought to isolate Tsai over her refusal to endorse the “one China” principle that designates Taiwan as a part of China.

Chinese President Xi Jinping is expected to speak about Taiwan on Wednesday at a gathering in Beijing to mark the 40th anniversary of a statement issued by China to open talks with the government in Taipei.

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