China's five-month suspension in US-Chinese military contacts to protest Washington's arms sales to Taiwan has ended with the visit this week of a U.S. Defense Department official, a top Chinese officer said Friday. However, in opening the discussions, the Defense Ministry's head of foreign affairs said military-to-military ties remained in a "difficult period," and demanded that the US remove unspecified obstacles to improvement. "We expect the US side to take concrete measures for the resumption and development of our military ties," Maj. Gen. Qian Lihua was quoted as saying by the official Xinhua News Agency. Such routine calls are generally seen as a form of protest against US military contacts with self-ruling Taiwan, which China regards as a renegade province to be reunified with the mainland by force if necessary. China put military exchanges on hold in October over a $6.5 billion US arms sale to Taiwan, including such advanced weaponry as Patriot missiles and Apache attack helicopters. China said the sale interferes with internal Chinese affairs and harms its national security.