China lodged a diplomatic protest with the U.S. on Saturday over a phone call between President-elect Donald Trump and Taiwanese leader Tsai Ing-wen, but blamed the self-ruled island Beijing claims as its own for the “petty” move.

The 10-minute telephone call with Taiwan’s leadership was the first by a U.S. president-elect or president since President Jimmy Carter switched diplomatic recognition from Taiwan to China in 1979, acknowledging Taiwan as part of “one China”.

China’s Foreign Ministry said: “We have already made solemn representations about it to the relevant U.S. side. It must be pointed out that there is only one China in the world. Taiwan is an inalienable part of China’s territory.”

The statement urged the careful handling of the Taiwan issue to avoid any unnecessary disturbances in ties.

“The one China principle is the political basis of the China-U.S. relationship,” it said.

The wording implied the protest had gone to the Trump camp, but the ministry provided no explanation.

Speaking earlier, hours after Friday’s telephone call, Chinese Foreign Minister Wang Yi pointedly blamed Taiwan for the exchange, rather than Trump, a billionaire businessman with little foreign policy experience.

“This is just the Taiwan side engaging in a petty action, and cannot change the ‘one China’ structure already formed by the international community,” Wang said at an academic forum in Beijing, China’s Foreign Ministry quoted him as saying.

“I believe that it won’t change the longstanding ‘one China’ policy of the United States government.”

In comments at the same forum, Wang noted how quickly President Xi Jinping and Trump had spoken by telephone after Trump’s victory, and that Trump had praised China as a great country.

During Friday’s discussion, Trump and Tsai noted “the close economic, political and security ties” between Taiwan and the U.S., according to the president-elect’s office.

Despite cutting formal diplomatic ties, Washington keeps friendly and non-official relations with Taipei.

But since coming to office this year, Tsai has refused to accept the “One China” concept, prompting Beijing to cut off all official communication with the island’s new government.

As he came under fire for the move, Trump defended his decision to speak with Tsai, saying the island’s president initiated the call and brushed off the resulting criticism.