A World Health Organization (WHO) team due to investigate the origins of Covid-19 in the city of Wuhan has been denied entry to China.
Two members were already en route, with the WHO saying the problem was a lack of visa clearances.
However, China has challenged this, saying details of the visit, including dates, were still being arranged.
The long-awaited probe was agreed upon by Beijing after many months of negotiations with the WHO.
The virus was first detected in Wuhan in late 2019, with the initial outbreak linked to a market.
WHO chief Tedros Adhanom Ghebreyesus said he was "very disappointed" that China had not yet finalised the permissions for the team's arrivals "given that two members had already begun their journeys and others were not able to travel at the last minute".
"I have been assured that China is speeding up the internal procedure for the earliest possible deployment," he told reporters in Geneva on Tuesday, explaining that he had been in contact with senior Chinese officials to stress "that the mission is a priority for WHO and the international team".
https://www.bbc.com/news/world-asia-china-55555466