Japan’s Kyodo News service said the ban would also affect Japanese travelers. A Japanese Foreign Ministry official said it was aware of the report and was holding unofficial discussions with Chinese authorities about possible measures being considered by Beijing. It would be “regrettable” if restrictions were imposed, the official said, speaking on customary condition of anonymity.

A brief notice posted online by the Chinese Embassy in Seoul said the ban would apply until South Korea lifted its “discriminatory measures on entrance by China” to the country.

No other details were given. China has threatened to retaliate against countries that require travelers from China to show a negative test result for COVID-19 taken within 48 hours prior to arrival.

The regulation appeared to apply to new applicants and said nothing about South Koreans currently holding visas in Beijing and other Chinese cities where companies such as Hyundai and Samsung have a large presence.

In a phone call with his South Korean counterpart, Chinese Foreign Minister Qin Gang “expressed concern” about the measures taken by South Korea and said he “hopes that the South Korean side will uphold an objective and scientific attitude.”

China’s announcement appeared to be grounded on its stiff demand for reciprocity in foreign relations. Around a dozen countries have followed the U.S. in requiring negative tests for travelers coming from China, which has lifted most of its “zero-COVID” restrictions for the first time in three years but also has been experiencing a major outbreak since last month.

At a daily news briefing, Foreign Ministry spokesperson Wang Wenbin defended China’s anti-pandemic measures, adding that “regrettably, a handful of countries, in disregard of science and facts and the reality at home, have insisted on taking discriminatory entry-restriction measures targeting China. China firmly rejected this and took reciprocal measures.”

Wang did not respond directly to questions about the suspension of visas for South Koreans and Japanese.

The World Health Organization and several nations have accused China of withholding data on its outbreak. The testing requirements are aimed at identifying potential coronavirus variants carried by travelers.

China’s ambassador to Australia said the response of those nations to China’s COVID-19 outbreak hadn’t been proportionate or constructive.

Xiao Qian told reporters in Canberra that China had shifted its strategy late last year from preventing infections to preventing severe cases. He said countries should use a science-based response.

“Entry restrictions, if they’re targeted at China, they’re unnecessary,” the ambassador told reporters.

“If you look at some other countries in the world and their policies toward China, I mean, their responsible measures toward China [are] not constructive. It’s not based on science. It’s not proportionate,” he said.

The online notice at the embassy in Seoul did not say why China singled out South Korea for retaliation, although Chinese President Xi Jinping’s deeply nationalistic government has long resented Seoul’s alliance with the U.S.

The once-cordial ties between South Korea and its biggest trading partner soured after China targeted businesses, sports teams and even K-pop groups to protest deployment of an advanced U.S. anti-missile system in South Korea. China fought on the side of North Korea in the 1950-1953 war and has remained a staunch supporter of Pyongyang amid its missile launches and nuclear tests.

China abruptly reversed its strict pandemic containment requirements last month in response to what it says was the changing nature of the outbreak. That came after three years of lockdowns, quarantines and mass testing that prompted street protests not seen in three decades in Beijing and other major cities.

The most optimistic forecasts say China’s business and consumer activity might revive as early as the first quarter of this year. But before that happens, entrepreneurs and families face a painful squeeze from a surge in coronavirus cases that has left employers without enough healthy workers and kept wary customers away from shopping malls, restaurants, hair salons and gyms.

The abrupt decision by Xi’s government to end controls that shut down factories and kept millions of people at home will move up the timeline for economic recovery, but might disrupt activity this year as businesses scramble to adapt, forecasters say.

China is now facing a surge in cases and hospitalizations in major cities and is bracing for a further spread into less developed areas with the start of the Lunar New Year travel rush, set to get underway in coming days. While international flights are still reduced, authorities say they expect that domestic rail and air journeys will double over the same period last year, bringing overall numbers close to those of the 2019 holiday period, before the pandemic hit.