China denied entry to two members of a World Health Organization team investigating the origins of the novel coronavirus after both tested positive for COVID-19 antibodies, the Wall Street Journal reported.

Chinese officials blocked the duo from boarding their plane to the central Chinese city of Wuhan after they tested positive for the antibodies in blood-based serology tests during transit in Singapore, the report said, citing citing people familiar with matter.

“Relevant epidemic prevention control requirements will be strictly enforced,” Chinese foreign ministry spokesman Zhao Lijian told a regular news briefing, when asked about the report.