There were 38 people on board when the boat docked near Sfax on Thursday on a planned route to Italy, according to a court source.
Sub-Saharan migrants living in Tunisia have been under pressure since President Kais Saied gave a fiery speech last month in which he accused migrants of posing a demographic threat and of being behind a crime wave.
On Friday, a volunteer group that helps match rescue workers with migrants in distress at sea said 40 people were in danger on a boat “trying to flee Tunisia”. People pretending to be part of the coast guard removed the engine and beat some migrants, according to the volunteer group.
At least four fatal boat accidents have occurred in March in Tunisian waters.