ALGIERS (Reuters) - Algeria’s defence ministry said on Wednesday it had detained a suspected jihadist militant who was released this month by Mali as part of a prisoner swap, underscoring its fears of insecurity in the Sahel region. Mustapha Derar, an Algerian national, was arrested in Tlemcen after security forces tracked him from his crossing of the border into Algeria, the ministry said in a statement. Derar had joined a terrorist group in 2012, it added. Mali, grappling with an Islamist insurrection, released scores of prisoners including suspected militants early this month, days before jihadists freed four hostages: a Malian politician, a French aid worker and two Italians. Malian authorities have neither confirmed nor denied that militants were released in exchange for Soumaila Cisse, Sophie Petronin, Pierluigi Maccalli and Nicola Chiacchio. Algeria defeated its own Islamist insurgency in the 1990s in a civil war that killed 200,000 people. Its defence ministry said Mali’s release of militants was “impeding efforts to combat terrorism”. Both al Qaeda and the Islamic State groups have taken advantage of local conflicts to establish a presence across the Sahara and the Sahel region to its south.