BEIJING, Aug. 23 (Xinhua) -- China has made serious demarches to the U.S. side on Indiana Governor Eric Holcomb's visit to Taiwan, a Chinese foreign ministry spokesperson said on Monday. Taiwan is an inalienable part of China's territory. The Taiwan question has always been the most important and the most sensitive issue at the heart of China-U.S. relations, the spokesperson said when answering a media query regarding the visit. The Chinese side firmly opposes official U.S. exchanges with the Taiwan region in any form and under any name, the spokesperson said. "We urge relevant party in the U.S. to abide by the one-China principle and the three China-U.S. joint communiques and stop all forms of official interactions with the Taiwan region," the spokesperson said.  ■