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".
Last week, the Washington Post 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.
"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," a state department spokesperson told Vice News on Wednesday.
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.
However he emphasised that these tests were only needed for certain people such as those under quarantine.
Potty mouth jokes rife on Chinese social media
Analysis by Kerry Allen, BBC China media analyst
It was quite an unusual moment for Chinese netizens to hear the foreign ministry spokesman, Zhao Lijian, talk about anal swabbing.
It's igniting significant chatter on Chinese social media platform Sina Weibo. In particular, a lot of users are joking about how Americans are so potty-mouthed when it comes to China, that it would be expected they would mistake an oral swab for an anal one.
Some question the authenticity of the US diplomats' claims, and perceive that this is yet another "rumour" to "discredit" China over its Covid-19 handling.
There has been a lot of bad sentiment between China and the US over the last year. China has criticised the US government under former president Trump for exacerbating anti-Chinese sentiment by repeatedly calling Covid-19 the "China virus" and "Kung flu", and downplaying China's Covid-19 successes.
Many in China are of the view that the US needs to do some self-reflection on its own handling of the virus, before preaching on decency.
"500,000 American people are dead," says one user, referencing the US' Covid-19 death toll. "Is that dignity?"