The Obama administration has formally notified congress of a $US1.83 billion ($A2.54 billion) arms sale package for Taiwan, drawing an angry response from China.
The authorisation came a year after the US Congress passed legislation approving the sale. It is the first such major arms sale to Taiwan in more than four years and includes two frigates, anti-tank missiles, amphibious assault vehicles and other equipment.
The White House said there was no change in the longstanding US "one China" policy. Past US weapons sales to Taiwan have attracted strong condemnation in China, which considers Taiwan a renegade province.
The White House said the authorisation followed previous sales notifications by the administration totalling more than $US12 billion under the Taiwan Relations Act.
"Our longstanding policy on arms sales to Taiwan has been consistent across six different US administrations," National Security Council spokesman Myles Caggins said. "We remain committed to our one-China policy," he added.
Although Washington does not recognise Taiwan as a separate state from China, it is committed under the Taiwan Relations Act to ensuring Taipei can maintain a credible defence.
The sales come at a period of heightened tension between the US and China over the South China Sea, where Washington has been critical of China's building of man-made islands to assert expansive territorial claims.
China summoned the US charge d'affaires in Beijing, Kaye Lee, to protest and said it would impose sanctions on the companies involved, state news agency Xinhua reported.
"Taiwan is an inalienable part of China's territory. China strongly opposes the US arms sale to Taiwan," Xinhua quoted Vice Foreign Minister Zheng Zeguang as saying.
Zheng said the sales went against international law and basic norms of international relations and "severely" harmed China's sovereignty and security.
"To safeguard our national interests, China has decided to take necessary measures, including imposing sanctions against the companies involved in the arms sale," Zheng said.
The US State Department said Raytheon and Lockheed Martin were the main contractors in the sales.
It was not clear what impact sanctions might have on the companies, although in 2013, Lockheed Martin signed a pact with the Thailand-based Reignwood Group to build an offshore plant to supply energy for a luxury resort on Hainan island in southern China.
However, previous Chinese sanction threats have not been followed up by Beijing.
Taiwan's defence ministry said in a statement the new weapons would be phased in over a number of years and would enable Taiwan to maintain and develop a credible defence.
US State Department spokesman John Kirby said the decision was based solely on Taiwan's defence needs.
"The Chinese can react to this as they see fit," he said. "This is nothing new. ... There's no need for it to have any derogatory effect on our relationship with China."
Kirby said Washington wanted to work to establish a "better, more transparent more effective relationship" with China in the region and had been in contact with both Taiwan and China on this on Wednesday. He declined to elaborate.
Analysts and congressional sources believe the delay in the formal approval of the sales was due to the Obama administration's desire to maintain stable working relations with China, an increasingly powerful strategic rival but also a vital economic partner as the world's second-largest economy.
