BEIJING (AP) — China vowed Wednesday that it will make a “proper and necessary response” if the U.S. proceeds with its latest planned arms sale to Taiwan.

Foreign ministry spokesperson Wang Wenbin said the sale of $600 million in armed drones to the island “brutally interferes in China’s internal affairs and seriously undermines China’s sovereignty and security interests.”

The U.S. should cancel all such sales to Taiwan “so as to avoid further damage to China-U.S. relations and peace and stability in the Taiwan Strait,” Wang told reporters at a daily briefing.

China, which claims Taiwan as its own territory, will make a “proper and necessary response according to the development of the situation,” Wang said.

The State Department said Tuesday it had greenlighted Taiwan’s purchase of four “weapons ready” remotely piloted aircraft and related equipment, the latest in a series of arms transfers for the island.

In its announcement, the department said the proposed sale “serves U.S. national, economic, and security interests by supporting the recipient’s continuing efforts to modernize its armed forces and to maintain a credible defensive capability.”

Just last week, the administration approved plans for a $2.37 billion sale of Harpoon missile systems to Taiwan. That came hours after Beijing had announced sanctions on U.S. defense contractors, including Boeing, the lead contractor on the Harpoon deal, over a previous weapons deal.

China’s ruling Communist Party threatens to use force to annex Taiwan, which it has regarded as a breakaway province since the sides split amid civil war in 1949. Washington maintains only unofficial ties with Taipei in deference to Beijing but remains the islands most important source of weaponry and is legally bound to ensure its armed forces can mount an adequate defense.

Chinese-U.S. relations have plunged to their lowest level in decades amid disputes about security, technology, the coronavirus pandemic and human rights. At the same time, China has stepped up military flights into Taiwanese airspace in what it calls a warning to the pro-independence administration of President Tsai Ing-wen, further bolstering bipartisan political support for Taiwan in the U.S.