Human traffickers increasingly use Tunisia as a launch pad for migrants heading for Europe as Libya's coast guard, aided by armed groups, has tightened controls.
Tunisia's navy stopped boats with migrants departing from beaches in the south and north of the country, arresting 555 people in September, the data showed. In August only 170 people had been caught trying to depart from Tunisia by boat.
"We succeeded in foiling many attempts, which have increased significantly as the weather improves and smugglers are promoting that journeys coming out of Tunisia are more safe than other destinations," Colonel Major Khelifa Chibani of Tunisia's national guard told Reuters.
He said pregnant women and children had been among the migrants caught while trying to depart by boat.