China has threatened to impose sanctions on US firms involved with the sale of F-16 fighter planes to Taiwan if Washington goes ahead with the deal.
Foreign Ministry spokesman Geng Shuang urged the US to stop the arms sales and end military contact with Taiwan.
The US government has approved the possible $8bn (£6.6bn) deal involving 66 aircraft, the biggest in decades.
The potential sale comes amid ongoing tensions between Washington and Beijing, notably over trade.
China regards Taiwan as part of its territory which should be reunited with the mainland, by force if necessary.
It has regularly criticised US arms deals with Taiwan including the current one, which has been widely discussed.
The US Defense Security Cooperation Agency announced the deal on Tuesday in an official notification to Congress.
In a statement, it said that the deal was for 66 F-16 fighter aircraft, 75 General Electric engines and other systems.
The sale was in US national interests and would help improve Taiwan's security, it added.
Quoted by Chinese state media, Mr Geng said the sale was a violation of international law and international relations, as well as the One China policy - under which the US recognises and has only formal ties with China and not Taiwan.
China would take all necessary measures to safeguard its own interests, he added, including imposing sanctions on firms involved in the deal.