China's foreign ministry denied on Thursday that U.S. diplomats in the country had been required to take anal swab tests for COVID-19, following media reports that some had complained about the procedure.

U.S. media outlet Vice on Wednesday cited a State Department official as saying the test was given in error and that China had said it would stop such tests on U.S. diplomats.

"To my knowledge...China has never required U.S. diplomatic staff stationed in China to conduct anal swab tests," foreign ministry spokesman Zhao Lijian told a daily news briefing in Beijing.

In an email to Reuters, a State Department representative said it was "committed to guaranteeing the safety and security of American diplomats and their families, while preserving their dignity".

Some Chinese cities used samples taken from the anus to detect potential infections amid stepped-up screening during a spate of regional outbreaks ahead of the Lunar New Year holidays.

Tests using anal swabs can avoid missing infections as virus traces in faecal samples or anal swabs could remain detectable for a longer time than in those from the respiratory tract, Li Tongzeng, a respiratory diseases doctor in Beijing, told state television last month.

Stool tests may also be more effective in finding infections in children and infants as their waste carries a higher viral load than adults, researchers at the Chinese University of Hong Kong said in a paper published last year.