Hong Kong has closed its trade office in Taipei, the latest tit-for-tat exchange between the cities as Beijing works to isolate the democratically ruled island.

The government of the former British colony said in a statement Tuesday it had “temporarily suspended operations” of the Hong Kong Economic, Trade and Cultural Office, without giving a reason. The closure is unrelated to the recent rise in Covid-19 cases in Taiwan, a Hong Kong government spokesperson said in an email.

The relationship between Hong Kong’s China-appointed officials and the administration of Taiwanese President Tsai Ing-wen—a vocal supporter of pro-democracy protesters in Hong Kong—has been tense for nearly a year, impacting the informal diplomatic offices that have served as communication conduits between the two sides of the Taiwan Strait. Last week the Taiwan office that handles affairs related to China complained that Hong Kong officials were dragging their feet on new work permits for employees of its office in the city, the South China Morning Post reported.

“It is really unfortunate and regrettable that the Hong Kong government would make such a move,” said Alexander Huang, a professor of international relations at Tamkang University in New Taipei City. “It really serves no one’s interests, especially the people of Hong Kong and Taiwan, and it makes the future of bilateral ties more inconvenient.”

The decision raises the chances that Taiwan responds by closing its office in Hong Kong, Huang added.

Taiwan’s Mainland Affairs Council called Hong Kong’s decision “regretful.” It added in a statement that the office in Hong Kong would continue functioning normally.

Junior employees of Taiwan’s Hong Kong representative office faced difficulties getting visas last summer, while Taiwan withheld work permit renewals for staff in Hong Kong’s office in Taipei. China had earlier insisted that Taiwan officials serving in Hong Kong sign a statement agreeing that both sides belong to “one China,” leading to the exit of Taipei’s top envoy.

Beijing has taken steps to isolate Taiwan since Tsai was elected in 2016 and refused to endorse Beijing’s “one China” principle.

China at the same time has been applying increasing military pressure to Taiwan, a move that comes as Taipei boosts ties with Washington. The Chinese air force sent 25 warplanes over the Taiwan Strait on April 12, the largest such sortie this year.

The Communist Party ruling China sees Taiwan as territory that must be seized by force if necessary. Taipei rejects this, saying Taiwan is already a de facto sovereign nation.