Libyan gunmen kidnapped five Tunisian fuel smugglers near the border on Saturday and Tunisian authorities temporarily closed the main crossing of Ras Jder pending negotiations for their release, a Tunisian security source said.
The source said gunmen from the western Libyan town of Zuwara, which saw days of clashes between rival militias last week, were believed to be holding the Tunisians hostage inside Libya.
"It is not political," the source said, adding that the incident was believed to be connected to the rampant smuggling business between Libya and Tunisia.
He said talks were under way with the Libyan army to secure their release.
The incident highlighted the challenges Libya's National Transitional Council has faced in imposing its authority over myriad militias since last year's revolt ousted Muammar Gaddafi after 42 years in power.
At least 18 people were killed in clashes between rival militias in Zuwara last week, which only ended after the government sent in troops to impose a ceasefire.
The border crossing at Ras Jder has been closed several times over the past year due to clashes or unrest in the frontier area.