China's foreign ministry said on Monday Chenyue Mao, the Wells Fargo banker who has been blocked from leaving the country, was involved in a criminal case and was obliged to cooperate with the investigation.

China has prevented a Wells Fargo banker from leaving the country, the American bank said, adding to concerns about travel there as tensions with Washington remain high. A Wells Fargo spokesperson said the bank was “closely tracking this situation and working through the appropriate channels so our employee can return to the United States as soon as possible”.

A Wells Fargo executive who was born in Shanghai and works in Atlanta has been detained in China for reasons unknown. Chenyue Mao, a managing director at Wells Fargo, has been banned from leaving the country,