US lawmakers voted to greenlight an agreement aimed at deepening economic relations with Taiwan, prompting an irritated response from Beijing on Thursday.

The US-Taiwan Initiative on 21st Century Trade streamlines customs checks, looks to improve regulatory procedures and establishes anticorruption measures.

After the House of Representatives approved it on Wednesday, it now heads to the Senate, the upper chamber of the US Congress, where it is expected to be ratified.

China said Thursday that the move "seriously contravenes the US side's stated commitment to maintain only unofficial relations with Taiwan".

Beijing "resolutely opposes" any nations with which it has diplomatic ties signing agreements "with connotations of sovereignty or of an official nature with China's Taiwan region," the foreign ministry told AFP in a statement.

"The US should... stop promoting and immediately withdraw (the agreement), and stop sending erroneous signals to 'Taiwan independence' separatist forces," the ministry said.

Washington does not have official diplomatic relations with self-governing Taiwan, which China claims as part of its territory and has vowed to one day seize -- by force if necessary.

The governments maintain unofficial ties, however, through the de facto US embassy on the island, the American Institute in Taiwan, which signed the agreement earlier this month with the Taipei Economic and Cultural Representative Office in the United States.

Washington has remained a key ally and arms supplier to Taiwan despite switching diplomatic recognition from Taipei to Beijing in 1979. It is also the island's second-largest trade partner.

In April, Beijing conducted three days of military exercises simulating a blockade of the island in response to US House of Representatives Speaker Kevin McCarthy and Taiwanese leader Tsai Ing-wen meeting in California.

AFP