China has denied that it required US diplomats to undergo anal swab tests for coronavirus.
US media reported that diplomats had complained after being made to undergo the procedure. Some Chinese cities have introduced anal swabs, with experts there claiming they can "increase the detection rate of infected people".
The country has largely brought the virus under control.
China's foreign ministry spokesperson Zhao Lijian denied the claims on Thursday, telling a press conference that "China has never required US diplomatic staff stationed in China to conduct anal swab tests".
It was recently reported that some workers had told the US state department that they had been subjected to the tests. Anal swabs involve inserting a cotton swab 3-5cm (1.2-2.0 inches) into the anus and gently rotating it. It is not known how many US diplomats may have had the test.
A state department spokesperson said: "The State Department never agreed to this kind of testing and protested directly to the Ministry of Foreign Affairs when we learned that some staff were subject to it,"
The state department added that it was told by Beijing that the test was given "in error".
China introduced anal swabs in January. Li Tongzeng, a respiratory and infectious disease doctor in Beijing told state media that anal tests can avoid missing infections as virus traces are detectable for a longer time than the more common Covid tests used in the mouth and nose.
He did, however, emphasise that these tests were only needed for certain people such as those under quarantine.