China has made serious démarches to the U.S. side over Indiana Governor Eric Holcomb's visit to China's Taiwan region, the Chinese Foreign Ministry said on Monday.

China has always firmly opposed official U.S. exchanges with Taiwan in any form and under any name, said a Foreign Ministry spokesperson.

Noting that Taiwan is an inalienable part of China's territory, the spokesperson said the Taiwan question has always been the most important and the most sensitive issue at the heart of China-U.S. relations.

China urges relevant parties in the U.S. to abide by the one-China principle and the three China-U.S. joint communiqués and to stop all forms of official contact with the Taiwan region, the spokesperson added.

Holcomb's visit marked the third trip to the Taiwan region this month by a U.S. delegation. Earlier, U.S. House Speaker Nancy Pelosi and U.S. lawmakers led by Senator Ed Markey also visited China's Taiwan region.

(Cover: View of the Taipei 101 skyscraper in Taipei, China's Taiwan region. /CFP)