China has said it lodged “serious” complaints with the Japanese government after a leader from its ruling political party made a trip to Taiwan, insisting the island is part of its sovereign territory while demanding an end to all direct diplomacy with Taipei.

press briefing, Chinese Foreign Ministry spokesman Wang Wenbin said Beijing considers the move “provocative,” accusing some Japanese politicians of arranging public “stunts” for their own “selfish political gains.”

“China firmly opposes this and has made serious demarches to the Japanese side,” he continued. “We urge Japan to uphold the one-China principle, … stop all forms of official contact with the Taiwan region, and stop sending wrong signals to ‘Taiwan independence’ separatist forces.”

Reaching Taiwan on Monday, the Japanese delegation was led by Hiroshige Seko, secretary-general for the Liberal Democratic Party and formerly Minister of Economy, Trade and Industry under the late Prime Minister Shinzo Abe. Seko held discussions with a number of senior officials, including Taiwanese President Tsai Ing-wen, who voiced hopes for additional “exchanges in the field of security,” according to local media.

Seko similarly stressed that it is “necessary to further develop ties,” arguing Taiwan and Japan share “common values,” but added that “efforts need to be made for peace and stability in the region.”

Wang went on to criticize Japan’s colonial history, saying that while Taiwan was once under Tokyo’s rule, it is an “inalienable part of China’s territory.” He also warned Taipei’s leadership that “any attempt to go against the trend of history and solicit foreign support in seeking ‘Taiwan independence’ is doomed to fail.”

Seko’s visit was preceded by another trip to Taipei by Liberal Democratic Party policy chief Koichi Hagiuda earlier in December, one among a series of high-profile foreign visits in recent months. Chinese officials have repeatedly condemned such junkets, and carried out unprecedented military drills over the summer following a trip by US House Speaker Nancy Pelosi. Similar exercises were launched in the airspace and waters around Taiwan earlier this week.