China has criticised the UK, US and other governments for congratulating the winner of Taiwan's presidential election.
Beijing accused several nations of "interfering in China's internal affairs" after world leaders sent messages to president-elect Lai Ching-te following his victory on Saturday.
China, which claims Taiwan as part of its territory and considers it a breakaway province, has accused Mr Lai and his Democratic Progressive Party (DPP) of being dangerous separatists.
The DPP says it favours the status quo of the island being self-governed but has not publicly called for independence.
The party's win has been seen as a setback for Beijing and tensions heightened further on Sunday as it accused US secretary of state Antony Blinken of "sending a gravely wrong signal" after he sent his best wishes to the winner.
It came after Mr Blinken said: "We congratulate Dr Lai Ching-te on his victory in Taiwan's presidential election. We also congratulate the Taiwan people for participating in free and fair elections and demonstrating the strength of their democratic system."
But China's foreign ministry said it "strongly deplored and firmly opposed" the comments - and added that "serious representations to the US side" had been made.
"We urge the US to stop interactions of an official nature with Taiwan and stop sending any wrong signal to the separatist forces for 'Taiwan independence'," a spokesperson added.
Tensions have been further ramped up by a visit to Taipei by former US national security adviser Stephen Hadley and former deputy secretary of state James Steinberg on Sunday.
The pair are due to hold a string of meetings with political leaders, but are said to be doing so in a "private capacity".
The US does not officially recognise Taiwan as an independent state and supports the status quo, although US President Joe Biden has promised to defend it from a possible attack by China.
It comes after Beijing also condemned the "incorrect actions" of Foreign Secretary Lord Cameron after he also congratulated Mr Lai - and described the elections as a "testament to Taiwan's vibrant democracy."
A Chinese embassy statement said on Saturday: "We urge the United Kingdom to acknowledge the position that Taiwan is a province of China, cautiously handle Taiwan-related matters in accordance with the one-China principle, [and] stop any remarks that interfere in China's internal affairs."
The Chinese government further criticised a similar message from the Japanese government, and also hit out at France - even though officials in Paris did not name Lai or his party, and instead congratulated "all voters and candidates".
On the eve of the election Chinese diplomats also warned Western nations of the unspecified dangers of supporting "Taiwan independence forces".
Xiao Qian, Chinese ambassador to Australia, published an article in The Australian on Friday which said: "If Australia is tied to the chariot of Taiwan separatist forces, the Australian people would be pushed over the edge of an abyss."
Mr Lai's victory means the DPP will continue to hold the presidency for a third four-year term, following eight years under President Tsai Ing-wen. He will take office in May.