AFP reports that Beijing on Saturday warned the US that the One China policy was non-negotiable, after Donald Trump suggested he could abandon the decades-old diplomatic principle and boost ties with Taiwan. "It is not up for negotiation," Chinese Foreign Ministry spokesman Lu Kang said in a statement. "There is only one China in the world, Taiwan is an inalienable region of China, and the government of the People's Republic of China is the only legitimate government representing China." Trump has threatened to get tough with what he sees as unfair Chinese trade practices, and suggested that the One China policy could become a bargaining chip. "Everything is under negotiation, including One China," he told the Wall Street Journal in an interview published Friday. Trump has already irked China by accepting a congratulatory phone call from Taiwan President Tsai Ing-Wen after he won the presidential election, upending decades of diplomatic precedent in which the White House has foregone direct communication with the leader of Taiwan.