Bulgarian authorities say one of the organisers of this week’s riots at a refugee shelter belongs to a ‘radical cell’.
The person’s identity and nationality have not been revealed, neither has the nature of the radicalisation.
Clashes broke out after a health scare at the camp prompted authorities to seal it off and prevent migrants from leaving.
More than 400 asylum seekers were arrested at the centre in the southern town of Harmanli, near the Turkish border.
From December, Bulgaria will begin extraditing a number of those detained to their native Afghanistan, Prime Minister Boiko Borisov announced on Friday.