AN improvised explosive device killed four Tunisian soldiers patrolling in a mountain region near the Algerian border, Defence Ministry spokesman Mohammed Zekri said. The mountainous Moghila area, near the impoverished city of Kasserine, is home to an Islamist militant group that the Tunisian army has been fighting for years. Tunisia faces a small but persistent militant threat, foreign diplomats focused on security say. As well as jihadist cells holed up in remote mountain regions, who have not made successful forays beyond their strongholds in recent years, there is also a threat from militants radicalised online. Last year militants tried to…