Libya transported 142 illegal migrants back to Guinea with the help of the UN migration agency, officials said.
The number of people stuck in Libyan detention centres has risen dramatically this year after armed groups largely shut down the boat route to Italy from the smuggling hub of Sabratha.
The International Organisation for Migration flew the Guinean migrants from two western cities to the city of Misrata, from where they boarded a plane for Conakry.
The deportations come in the wake of a CNN report on migrants being sold for slave labour that sparked an international outcry.
Migrant flows through Libya have surged since 2014.
No fewer than 600,000 people have crossed the central Mediterranean to Italy in the past three years, but departures from Libya’s coast dropped sharply in July when armed groups in Sabratha began preventing boats from leaving.
After clashes in the western city in September, thousands of migrants held near the coast emerged and were transferred to detention centres under the nominal control of the UN-backed government in Tripoli.
Amnesty International said this month that up to 20,000 people are being held in detention centres and are subject to “torture, forced labour, extortion, and unlawful killings”.
Other human rights organisations have said similar things in recent months.