China on Thursday denied subjecting U.S. diplomats to COVID-19 anal tests following reports from Washington that some of its personnel were being made to undergo the procedure.

Chinese Foreign Ministry spokesperson Zhao Lijian told reporters at a daily briefing that “China has never asked U.S. diplomats in China to go through anal swab tests.”

A U.S. State Department spokesperson said Washington was “committed to guaranteeing the safety and security of American diplomats and their families while preserving their dignity, consistent with the Vienna Convention on Diplomatic Relations as well as other relevant diplomatic law provisions.”

The Washington Post reported last week that some U.S. personnel had told the department they had been subjected to the anal tests.

The procedure has been applied in China because it is reportedly more accurate than nasal or mouth swabs.

China has not reported a new local case of COVID-19 in more than a week, but has maintained strict testing, especially for people arriving from abroad. Diplomats and other foreigners with special status are exempted from a ban on most foreigners entering the country.