Tunis - Tunisia said on Monday that it was negotiating for the release of 172 nationals being held by a Libyan militia as bargaining chips for one of its commanders detained in Tunis.The foreign ministry's Arab and African affairs chief Touhami Abdouli said the Tunisians had been detained in western Libya by a militia that is part of the Libya Dawn alliance which controls the capital Tripoli and third city Misrata."We are going to try to make the effort to resolve this at the political level," Abdouli told Shems-FM radio. "I am optimistic."The Tunisian consul in Tripoli, Ibrahim Rezgui, told Jawahra FM radio late Sunday that he had received complaints from Tunisian citizens about the arrests."Around 172 are being held by a militia allied to Libya Dawn... but there could be more," said Rezgui."They are being held in the district of Salaheddine [in the Tripoli region] and we are in contact with Libyan authorities" about their well being, he added.Rezgui said the Tunisians were arrested "in retaliation for the arrest on Thursday in Tunis of one of their leaders," Walid el-Klibi."Tunisian authorities are investigating this individual and if the judiciary finds nothing against him it will order his release," he added.Libya has been wracked by conflict since the 2011 overthrow of veteran dictator Muammar Gaddafi in a Nato-backed uprising, with rival governments and powerful militias battling for power.