According to a statement by the bank released on Thursday, the incident happened two weeks ago in the capital, Addis Ababa.

The unnamed staff members were detained for many hours - without any official explanation - until, on learning of their arrest, Prime Minister Abiy Ahmed intervened and ordered their immediate release, the bank’s statement said.
The AfDB called the occurrence “a very serious diplomatic incident,” adding it had lodged a formal complaint with the authorities.

The bank is one of Ethiopia’s key financial partners and its chief, Akinwumi Adesina, enjoys warm relations with Prime Minister Abiy.

In September, the AfDB approved more than $100m (£80m) in funding to finance power supply improvements in Ethiopia.

Security forces have not commented on the allegations and the BBC’s attempts to get a response have not been successful.