The United States officially opened its new “American Institute in Taiwan” (AIT) complex in Taipei on Tuesday, in a ceremony attended by senior U.S. and Taiwanese officials, including Taiwan’s President Tsai Ing-wen.

China formally protested the ceremony as a “serious violation of the ‘One China’ principle” and said it “negatively impacts China-U.S. relations.”

“AIT’s new home is both a tangible symbol that reflects the strength of our ties and a state-of-the-art facility that will make possible even greater cooperation for years to come,” said Assistant U.S. Secretary of State for Educational and Cultural Affairs Marie Royce at the opening ceremony.

“As free and open democracies, we have an obligation to work with one another to defend our values and protect our joint interests. As long as we stand together, nothing can come between us,” President Tsai declared.

The complex is an impressive five-story structure that underwent a $250 million renovation. The American Institute has functioned as a de facto U.S. embassy since 1979, housed in much less elaborate facilities until now.

“The friendship between Taiwan and the US has never been more promising. The great story of Taiwan-US relations remains to be filled with the efforts of those that will one day occupy this building,” Tsai said to emphasize the importance of the new offices.

The New York Times notes there was speculation President Trump originally planned a “bolder show of support for Taiwan,” perhaps by sending a Cabinet-level official to attend the ceremony, but reconsidered in light of delicate trade negotiations with China and his summit meeting with North Korea’s Kim Jong-un. At the opening ceremony, American Institute chairman James Moriarty referred to the Singapore summit and said it was important to respect its significance.

China’s state-run Global Times nevertheless unloaded a furious editorial against the American Institute in Taiwan on Monday, grousing that even though Trump did not send someone who would have utterly enraged Beijing – such as National Security Advisor John Bolton – the presence of Assistant Secretary of State Royce was bad enough.

The Global Times expressed annoyance with the size of the AIT compound, the number of people who will be stationed there, the presence of U.S. Marine guards, and the possibility that higher-level U.S. officials could visit in the future thanks to the recently-passed Taiwan Travel Act. The editors were also concerned that the AIT could be used as a “bargaining chip of Washington against China” in trade negotiations.

“We must draw a red line for the US and Taiwan. Once crossed, a serious Taiwan Straits crisis will be triggered. For instance, visits by US warships to Taiwan or direct participation of American troops in Taiwan defense will disrupt the entire cross-Straits situation,” the Chinese paper growled.

“The reason why Washington is further activating Taiwan as a chess piece and Taiwan is desperately clinging to the US is because they found it more difficult to deal with the mainland. The mainland must continue to build up its deterrence against Taiwanese authorities, making them know that the US cannot be their savior,” the Global Times added.