The United States on Monday said it had approved a $2.4 billion sale of 100 Harpoon coastal defence systems to Taiwan, defying Beijing's anger over a $1 billion missile deal last week.
The announcement came just hours after Beijing said it would sanction US firms involved in an earlier arms sale to the democratic self-ruled island.
The proposed sale of the Harpoon systems "will help improve the security of the recipient and assist in maintaining political stability, military balance... and progress in the region," the State Department said in a statement.
The deal involves 100 Harpoon Coastal Defence Systems (HCDS), which includes 400 RGM-84L-4 Harpoon Block II surface-launched missiles with a range of around 125 kilometers.
The missiles, manufactured by Boeing, can be positioned on fixed platforms or mounted on trucks.
The office of Taiwan's President Tsai Ing-wen released a statement thanking the United States for the sale, saying it would "upgrade asymmetric warfare capabilities."
Democratic and self-ruled Taiwan lives under constant threat of invasion by authoritarian China, whose leaders view the island as part of their territory.
They have vowed to one day seize Taiwan, by force if necessary.
Beijing has ramped up diplomatic and military pressure on Taiwan since the 2016 election of Tsai, who views the island as a de facto sovereign nation and not part of "one China."
Chinese fighter jets and bombers have entered Taiwan's air defence zone with unprecedented frequency in recent months, while propaganda films have shown simulated attacks on Taiwan-like territories and US bases in Guam.
Beijing said Tuesday it "firmly opposed" such moves, urging the US to "call off the relevant arms sales plan to Taiwan, so as not to cause further damage to China-US relations and peace and stability across the Taiwan Strait".
Foreign ministry spokesman Wang Wenbin said China would "take proper and necessary measures to firmly safeguard its national sovereignty and security interests."
