China on Tuesday (Jul 9) urged the United States to "immediately cancel" a potential US$2.2 billion arms sales to Taiwan, saying it strongly opposes the action.

It would be the first bigticket US military sale to Taiwan in decades, and comes as ties between Washington and Beijing are already strained by their trade war.

China has lodged formal complaints through diplomatic channels expressing "strong dissatisfaction and resolute opposition" to the move, China's foreign ministry spokesman Geng Shuang said at a regular press briefing.

"The sale of weapons by the United States to Taiwan ... seriously violates the oneChina principle ... grossly interferes in China's internal affairs and undermines China's sovereignty and security interests," Geng said at a daily news briefing in Beijing.

"China urges the US to ... immediately cancel the planned arms sale and stop military relations with Taipei to avoid damaging SinoUS relations and harming peace and stability in the Taiwan Strait," he added.

The proposed sale includes 108 M1A2T Abrams tanks, 250 Stinger portable antiaircraft missiles, related equipment and support at an estimated cost of just over US$2.2 billion, according to the US Defense Security Cooperation Agency (DSCA).

It "will contribute to the modernisation of the recipient's main battle tank fleet", improve its air defense system and "support the foreign policy and national security of the United States by helping to improve the security and defensive capability (of Taiwan)," DSCA said.

It would not alter the "basic military balance in the region," the agency added, and Congress has been notified. US lawmakers have 30 days to object to the sale but are unlikely to do so.

Taiwan has been ruled separately from China since the end of a civil war in 1949, but Beijing considers it a part of its territory to be retaken by force if necessary.

China has significantly stepped up diplomatic and military pressure on Taipei since the election in 2016 of President Tsai Ingwen, whose Democratic Progressive Party refuses to acknowledge that the island is part of "One China".

It has also staged military exercises near the island, and steadily reduced the already small number of nations that recognise Taiwan.

The United States switched diplomatic recognition from Taiwan to China in 1979, but has remained an important ally and arms supplier to Taipei. Laws passed that year by Congress required Washington to provide the island with means of selfdefence.

But it has been wary of bigticket military equipment sales to Taiwan in recent years, fearful of stoking anger in Beijing.