China warned on Wednesday that any interference with or damage to the "one China" principle would have a serious impact on peace and stability in the Taiwan Strait, as Taiwan said maintaining peace was in everyone's interest.
U.S. President-elect Donald Trump said on Sunday the United States did not necessarily have to stick to its long-standing position that Taiwan is part of "one China", further upsetting China which was already angered by Trump's earlier telephone call with Taiwan President Tsai Ing-wen.
The issue is highly sensitive for China, which considers Taiwan a renegade province, and Beijing expressed "serious concern" about Trump's remarks.
An Fengshan, a spokesman for China's Taiwan Affairs Office, told a regular news conference the Taiwan issue was about China's sovereignty and territorial integrity.
"Upholding the 'one China' principle is the political basis of developing China-U.S. relations, and is the cornerstone of peace and stability in the Taiwan Strait," he said.
"If this basis is interfered with or damaged then the healthy, stable development of China-U.S. relations is out of the question, and peace and stability in the Taiwan Strait will be seriously impacted," An said.
Taiwan's policy-making Mainland Affairs Council said peaceful relations were a mutual responsibility across both sides of the Taiwan Strait.
"Taiwan has repeatedly stressed that maintaining peace and stability across the Taiwan Strait and throughout the region is in the best interests of all parties," said council spokesman Chiu Chui-cheng.
"Taiwan places equal weight on the development of Taiwan-U.S. relations and cross-strait relations."
China is deeply suspicious of Tsai and her ruling Democratic Progressive Party, believing they want to push for the island's formal independence, a red line for Beijing.
China has repeatedly warned that hard-won peace and stability across the narrow strait that separates them could be affected by any moves toward independence.
"I think the facts tell these people that Taiwan independence is a dead end," An said.
China has never renounced the use of force to bring Taiwan under its control, and some state media have suggested after Trump's remarks that a military solution may now be needed.
A senior U.S. defense official said on Tuesday Taiwan's defense spending had not kept pace with the threat posed by China and should be increased.
Taiwan's annual defense spending has not hit 3 percent of its gross domestic product in recent years, which some military and political experts in Taiwan have said should be a minimum level.
"Taiwan's defense spending factors in external threats and the nation's annual budget," Taiwan defense ministry spokesman Chen Chung-chi told Reuters.
"Our premier has said previously that the cabinet can look to use a special budget to meet defense needs in an emergency situation."In Beijing, Foreign Ministry spokesman Geng Shuang said the United States needed to handle the Taiwan issue cautiously to avoid ties with China receiving unnecessary interference.
"As for the so-called issue of Taiwan being threatened, I think we've said many times that we oppose the United States and Taiwan having any form of official contacts or military relations," Geng told a daily news briefing.
(Additional reporting by J.R. Wu in TAIPEI; Editing by Paul Tait and Lincoln Feast)