Expressing concern over a planned visit by a former American official to Taiwan for talks with the new government on the island, China on Monday asked the US to be cautious on the Taiwan issue and not medddle in China’s internal affairs.

Foreign Ministry spokesman Hong Lei said at a press briefing that China has already expressed concern over the planned Taiwan visit by US former Deputy Secretary of State William Burns , who is to meet with senior officials of Taiwan.

Hong reiterated that Taiwan is an inseparable part of Chinese territory and Taiwan affairs are China’s internal affairs.

Tsai Ing-wen, leader of the opposition Democratic Progressive Party (DPP) won the elections in Taiwan on Saturday, becoming the first woman president of Taiwan.

She was strong critic of pro-China Kuomintang (KMT) or Nationalist Party which lost the polls.  Hong asked the US to firmly abide by the one-China policy and the principles in the three Sino-US joint communiques, and live up to its commitment to opposing “Taiwan independence”.

“We urge the US side to do more things that are conducive to the stable development of China-US relations and peaceful development of relations across the Taiwan Strait, not vice versa,” Hong said.

Both China and Taiwan split in 1949 after the civil war. But Yaiwan has never declared independence and China still consider it as part of its territory awaiting reunification.

Meanwhile, China’s state-run Global Times today warned Tsai against pursuing a pro-independence path saying that formal split from the mainland would be a “dead end”.

Zhou Zhihuai, head of the Institute of Taiwan Studies at the Chinese Academy of Social Sciences, wrote in the daily that if Tsai “parts ways with the mainland, she will go down a dead end.

An editorial in English-language China Daily newspaper said that the Kuomintang lost the election due to issues such as rising unemployment and inequality, rather than its Beijing-friendly approach.

Tsai’s policy towards the mainland “remains ambiguous”. “She has a responsibility to keep the peaceful development of cross-Straits relations on track,” it said.