Beijing, March 21 (XINHUA) -- China urged the United States on Thursday to abide by the "one China policy", warning that any act to trample upon the Sino-U.S. Joint Communiques could result in a "very unfavorable" impact on relations between the two countries. The question of Taiwan, which relates to China's sovereignty and territorial integrity, is an essential and most important issue and is at the heart of Sino-U.S. relations, said Chinese Foreign Ministry spokeswoman Zhang Qiyue. China hopes the United States will not do anything against the spirit of the three Sino-U.S. Joint Communiques, she said. Zhang made the remarks at a news briefing in response to a question about the Taiwan official Tang Yiau-min's recent visit to the United States. Zhang replied that Chinese Vice Foreign Minister Li Zhaoxing has put forward China's stand on the matter while making strong representations to the U.S. government with the hope that the United States treats the matter seriousness it deserves. She said during the U.S. President Bush's working visit to China last month, state leaders of both countries agreed that Chinese President Jiang Zemin and Vice President Hu Jintao would visit the United States this year. However, within one month of Bush's visit, the U.S. has already done several things which are against the spirit of the three Sino-U.S. Joint Communiques. Zhu said the U.S. side should stop interfering in China's internal affairs by interfering in the Taiwan issue.