Turkey has banned all academics from leaving the country, cancelling their annual leave, as President Tayyip Erdogan's post-coup crackdown escalated to "exceptional proportions".

Teachers were told on Wednesday they could not travel abroad on any work-related trips for the foreseeable future and those currently overseas were ordered to return.

One British academic at a state-run university in Istanbul told the Telegraph that foreign nationals had also been told to come back to work.