China ramped up its rhetoric over Taiwan on Monday, describing any support for its independence as "doomed to fail", and threatened retaliation against US diplomatic visits to the island.

Taiwan has been ruled separately from China since the end of a civil war in 1949, but Beijing considers the island part of its territory awaiting reunification. The island is a flashpoint with Washington, which promises military support to the elected government and has sent two envoys to Taipei in as many months.

At a press briefing Monday, the foreign ministry said that the envoys' visits were a "political provocation" and threatened retaliation. "China will take appropriate countermeasures, including targeting relevant individuals," said foreign ministry spokesman Wang Wenbin, without elaborating.

He warned that the US actions will "further damage the cooperation" between the US and China. Wang added that any support for Taiwan's independence is a "dead end... doomed to fail".

Washington switched diplomatic recognition to Beijing in 1979. Beijing rejects any recognition of Taiwan and has mounted a decades-long policy of marginalising the democratic island.

Washington's increased outreach to Taiwan under President Donald Trump is among a catalogue of sore points with Beijing as the countries clash over issues including trade, security and the coronavirus pandemic.

The US Undersecretary of State for economic growth, energy and the environment Keith Krach wrapped up a trip to Taiwan at the weekend, following on the heels of a trip by US health chief Alex Azar in August.

Last Friday, Taiwan scrambled fighter jets as the Chinese military conducted exercises near the Taiwan Strait during Krach's visit. US Secretary of State Mike Pompeo accused China of "military blustering".