China said on Thursday it had summoned a senior US envoy in protest at Washington's announcement that it would sell two warships to Taiwan as part of a $1.8 billion arms deal.
The massive contract comes at a time of reconciliation between China and Taiwan -- separated since 1949 -- but also as Washington worries that Beijing is militarising part of the South China Sea.
Vice Foreign Minister Zheng Zeguang made "solemn representations" with Kaye Lee, the US charge d'affaires, Wednesday regarding the sale, according to a statement on the foreign ministry's website.
The US State Department said Wednesday it intended to sell Taipei two Perry-class Frigates, Javelin anti-tank missiles, TOW 2B anti-tank missiles, AAV-7 Amphibious Assault Vehicles and a range of other military equipment.
"China staunchly opposes America's sale of arms to Taiwan," China's foreign ministry said, adding the country would impose sanctions against any companies involved in the sale.
"China urges the US... to cancel plans to sell arms to Taiwan and stop US-Taiwan military contacts to avoid causing further damage to Sino-US relations and bilateral cooperation in important areas", it said.
In the meeting, Zheng warned Lee that the sale "severely goes against international law and the basic norms of international relations" and "severely harms China's sovereignty and security interests", the statement said.
Relations between Beijing and Taipei have warmed under current Taiwanese president Ma Ying-jeou of the Kuomintang party. But China refuses to renounce the right to use force should Taipei move to declare independence formally.
China and Taiwan split at the end of a civil war in 1949.
The US recognises China rather than Taiwan, but remains a main ally and leading arms supplier to the island, providing a source of continued tension with Beijing.
Washington angered Beijing in October when a US warship sailed close to artificial islets that China is building out into military bases in the South China Sea.
Washington has said China's transformation of the geographical features in the Spratly Islands poses a threat to freedom of navigation in the critical area.