China slammed US Secretary of State Antony Blinken for extending his congratulations to Taiwan’s new president and separately sanctioned a former US congressman who supported Taipei, underscoring how the island’s status divides the two superpowers.

“It’s a serious violation of the political commitment made by the US to maintain only cultural, commercial and other unofficial relations with the Taiwan region,” Foreign Ministry spokesman Wang Wenbin said Tuesday in response to Blinken’s comments at a regular press briefing in Beijing.

The remarks by the US’ top diplomat sent “a seriously wrong signal to the Taiwan separatist forces,” Wang said. He added that Beijing had filed a diplomatic complaint with Washington, and called on “the US to immediately correct their mistakes.”

Blinken congratulated Lai Ching-te on Monday shortly after he took over as Taiwan’s new president. The Biden administration official also said in a statement that his nation looked forward to working with Lai and others in the democratically run island of 23 million people “to advance our shared interests and values.”

Also on Tuesday, Beijing announced sanctions on former US Congressman Mike Gallagher, accusing him of interfering in China’s internal affairs and harming Chinese sovereignty, according to a statement on the Chinese Foreign Ministry’s account on WeChat.

The former chair of the House select committee on China’s Communist Party led a delegation to Taiwan in February, when he met then President Tsai Ing-wen. Gallagher called on Washington to arm the island “to the teeth” against Chinese military intimidation in an op-ed in January. 

China opposes nations it has official ties with having contact with Taiwan, which it views as part of its territory to be brought under its control eventually, by force if necessary. 

The US is Taiwan’s main political and military supporter, irking Beijing. US President Joe Biden has repeatedly pledged to defend Taiwan if China attacks.

Lai has signaled that during his four years in office he will follow many of the policies of his predecessor, Tsai, including embracing the US.

That stance means ties between Taipei and Beijing will likely remain tense in the coming years.