With the world’s attention focused a few thousand miles southwest, where President Donald Trump was shaking hands with North Korean leader Kim Jong Un at a historic summit in Singapore, diplomats and businesspeople gathered in Taiwan’s capital to mark another kind of milestone.

The U.S. unveiled a new representative office in Taipei Tuesday, establishing a de facto embassy in the self-ruled island amid its escalating tensions with China. Taiwan’s President Tsai Ing-wen attended the opening ceremony, where she reaffirmed her government’s commitment to its “vital relationship” with the U.S., Reuters reports.

The American Institute in Taiwan, built over nine years at a cost of about $250 million, is bankrolled by the U.S. government and staffed by diplomats, effectively making the complex an embassy all but in name. The U.S. severed official diplomatic ties with Taiwan in 1979 to uphold Beijing’s “One China” policy, which maintains that the breakaway territory is part of the People’s Republic and can be reunified by force, if necessary.

But the U.S. still enjoys a “robust unofficial relationship” with the island nation of 23 million people, according to the State Department. The Republic of China, as Taiwan is officially known, is also a major purchaser of American-made military hardware and is among the top 10 U.S. trade partners with $65.3 billion in total two way trade during 2016.

Read more: The U.S. Trade War with China Has Reached a Dangerous New Phase

But U.S.-Sino relations have soured in recent months among China’s militarization of the South China Sea and ongoing trade disputes between the world’s two leading economic powers. Further complicating matters, Trump broke diplomatic protocol after winning the 2016 presidential election by accepting a congratulatory telephone call from Tsai Ing-wen. In February, Trump signed into law the Taiwan Travel Act, which allows top U.S. officials to visit the island.

Tensions between Beijing and Taipei are also on the rise; over the last few months, China has reprimanded airlines and other businesses for referring to Taiwan as a nation and pressuring countries around the world to cut diplomatic ties.

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