The U.S. ambassador to the United Nations, Kelly Craft, will visit Taiwan next week for meetings with senior Taiwanese leaders, Taiwan’s government and the U.S. mission to the U.N. said, prompting China to warn they were playing with fire.

Beijing, which claims the self-governed island as its own territory, has been angered by stepped-up support for Taiwan from the outgoing Trump administration, including trips to Taipei by top U.S. officials, further straining Sino-U.S. ties.

Chinese fighter jets approached the island in August and September during the last two visits - by U.S. Secretary of Health and Human Services Alex Azar and U.S. Under Secretary of State for Economic Growth, Energy, and the Environment Keith Krach, respectively.

“During her trip, the Ambassador will reinforce the U.S. government’s strong and ongoing support for Taiwan’s international space in accord with the U.S. one-China policy that is guided by the Taiwan Relations Act, the three U.S.-PRC joint communiques, and the Six Assurances to Taiwan,” the U.S. mission to the United Nations said in a statement on Thursday.

She will be in Taiwan from Jan. 13 to 15, it added.

While the United States, like most countries, has no formal diplomatic ties with Taiwan, it is the island’s strongest international backer and arms supplier, being obliged to help provide Taiwan with the means to defend itself under the 1979 Taiwan Relations Act.

China said it was firmly opposed to the visit.

“We wish to remind the United States that whoever plays with fire will burn himself. The United States will pay a heavy price for its wrong action,” China’s U.N. mission said.

“China strongly urges the United States to stop its crazy provocation, stop creating new difficulties for China-U.S. relations and the two countries’ cooperation in the United Nations, and stop going further on the wrong path.”

Taiwan’s Foreign Ministry said on Friday that Craft, whom it called a “staunch friend”, would meet President Tsai Ing-wen and Foreign Minister Joseph Wu.

The visit is highly symbolic as Taiwan is not a U.N. member, because of objections by China, which views the island as one of its provinces and not a country, and that only Beijing has a right to speak for Taiwan on the international stage.

Taiwan says that right belongs to its democratically elected government, not China, and has complained of Chinese pressure preventing it from getting real-time information from the World Health Organization during the COVID-19 pandemic.

Craft will likely bring up that issue.

The U.S. mission said that while in Taipei she would give a speech on “Taiwan’s impressive contributions to the global community and the importance of Taiwan’s meaningful and expanded participation in international organisations”.

In a September post on Twitter, she called for Taiwan’s “full participation at the UN”, following a meeting with Taiwan’s de facto consul general in New York.