The Chinese Embassy in Seoul lodged a diplomatic protest over the South Korean parliamentary delegation’s visit to Taiwan in December, calling it a “serious violation” of the two countries’ bilateral relations.

“We urge Korea to adhere to the ‘One China’ policy and the spirit of the establishment of diplomatic relations between Korea and China and refrain from engaging in any ‘official exchanges with the Taiwan region,’” an embassy spokesperson said via a press release.

It added in its statement that China expresses “strong protest” and “firm opposition” over the delegation’s recent visit, saying the embassy has already expressed complaint to the South Korean government.

The Chinese Embassy also urged Seoul to take timely measures to address the negative impact of the visit.

The delegation of the South Korea-Taiwan inter-parliamentary friendship group led by Rep. Cho Kyung-tae of the ruling People Power Party stopped by Taiwan from Dec. 28-31, according to Taiwan’s foreign ministry.

Other members are Rep. Chung Woo-taik, deputy speaker of the National Assembly, Rep. Lee Dal-gon of the ruling party and Rep. Lee Won-wook of the main opposition Democratic Party.

The Taiwanese foreign ministry added that the delegates met with President Ing-wen and Legislative Speaker You Si-kun during their low-key four-day stint.

Seoul’s foreign ministry said there is nothing to be said at the government level about individual activities by the members of the National Assembly regarding China’s protest.

“The government’s position remains steady and consistent regarding the ‘One China’ Policy and is well aware of the fact that China understands our position,” said Lim Soo-suk, the spokesperson of Seoul’s foreign ministry, during a press briefing on Thursday.