Turkish authorities deported a BBC News correspondent on Thursday after detaining him for 17 hours and branding him a "threat to public order."
Mark Lowen had been in Turkey to cover mass street protests triggered by the arrest and jailing of Istanbul's Mayor Ekrem Imamoglu.
BBC News CEO Deborah Turness called the deportation "extremely troubling" and said the broadcaster would raise the issue with Turkish authorities.
Lowen, who previously lived in Turkey for five years, said his expulsion was "extremely distressing," adding that press freedom is essential to democracy.
The Turkish presidency's communications directorate said Lowen had not applied for accreditation with its office as required.