Despite not maintaining formal diplomatic ties with the island nation, the US continues to be its primary supplier of arms.
The US has approved the possible sale of $2.2bn in arms to Taiwan, including 108 Abrams tanks and 250 Stinger surface-to-air missiles, despite objections from Beijing.
The Pentagon said the sale of the weapons requested by Taiwan would not alter the basic military balance in the region.
China had earlier urged the US to avoid the sale, warning the move could harm the relationship between the two countries. The timing is especially sensitive as Washington and Beijing are in the midst of a bitter trade war.
The US Department of Defense notified Congress on Monday of the sale, which it said could also include mounted machine guns, ammunition, and other support equipment.
The United States has no formal ties with Taiwan but is bound by law to help provide it with the means to defend itself and is its sole foreign supplier of arms.
China sees Taiwan as a renegade province and is yet to rule out the use of force to bring it under its control.
Speaking in Beijing on Tuesday, Chinese foreign ministry spokesman Geng Shuang said US arms sales to Taiwan were a serious violation of international law and a "crude interference in China’s internal affairs, harming China’s sovereignty and security interests."
"China is strongly dissatisfied and firmly opposed to this and has already made stern representations to the US side," Geng told a daily news briefing.
"Taiwan is an inseparable part of China's territory and nobody should underestimate the Chinese government's and people's firm determination to defend the country's sovereignty and territorial integrity and oppose foreign interference."
Taiwan's Presidential Office expressed "sincere gratitude" to the US government for the arms sale.
"Taiwan will speed up investment on defence and continue to deepen security ties with the United States and countries with similar ideas," Chang Tun-han, a spokesman for Taiwan's president, said in a statement.
Taiwan President Tsai Ing-wen said in March that Washington was responding positively to Taipei's requests for new arms sales to bolster its defences in the face of pressure from China.
Taiwan's Defense Ministry confirmed it had requested those weapons and that the request was proceeding normally.
10-year military spending plan
Taiwan’s military budget is expected to swell to slightly over US$13.1bn by 2027, according to the South China Morning Post newspaper, as Taiwan move to improve its defence capacity against China’s threats.
Taiwan’s ruling government has listed US$11bn for this year’s defence budget, up 5.6 per cent from 2018. The figure still pales in comparison to Beijing’s US$177.5bn , which represents a 7.5 per cent growth on last year’s military spending.
Taiwan’s military spokesman Chen Chung-chi said last month that the defence ministry had worked out an incremental 10-year budget aimed to bolster the island’s defence capability and uphold the security of Taiwan.
China as one nation
Taiwan has been independent since after the Chinese Civil War ended in 1949.
China’s Communists took control of the mainland while the losing Nationalist side went on to form its own administration on the island of Taiwan, which remained under its control.
Beijing has since used its significant economic, political, and military might to pressure states not to recognise Taiwan. As a result, the small island state has few formal diplomatic ties.
Despite this, it maintains close ties with Washington, which does not officially recognise the state.