An update via The Soufan Group's e-briefing and this attack's importance:
Armed militants are suspected to have crossed into Tunisia from Libya on March 7, carrying out a series of coordinated attacks against Tunisian security forces in the eastern border town of Ben Gardane. The attacks targeted an army base, a national guard post, and a police station, leaving 53 dead—including 35 militants, 11 members of the security forces, and seven civilians.... the Tunisian government to construct a 125-mile wall along the border with Libya. However, based on the scale and coordination of the assault on security forces, the wall is hardly serving as a deterrent.

Checking a map I now know where the IS "hot spot" town of Ben Gardane is, near the Libyan border: