A diplomatic source and Libya's Tripoli-based Government of National Accord said 14 workers had been taken hostage.
"The foreign ministry is following the case of the Tunisian citizens... kidnapped by armed Libyan elements near Zawiya," Tunisia's foreign ministry said on its Facebook page.
Rights activist Mustapha Abdelkebir said the armed group behind Thursday's kidnapping was demanding the release of one of its members held in Tunisia.
"The minister has spoken to his Libyan counterpart to insist on the protection of the detainees, accelerate their release and ensure that they return safe and sound," Tunisia's foreign ministry said.
The GNA's interior ministry said it had set up a "crisis cell" in Zawiya to establish "the necessary measures and contacts to guarantee the security of these kidnapped (Tunisians) and (to ensure) their release without conditions".
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Libya has been mired in chaos since the fall of dictator Moamer Kadhafi in a 2011 NATO-backed uprising, as two rival administrations and numerous militias grapple for power.