Authorities in western Libya released 120 fighters from a rival eastern force on Wednesday, the latest move towards reconciliation in a UN-backed peace process aimed at ending years of violence.

The men were fighting for the 107th Brigade under the command of eastern military strongman Khalifa Haftar, who in April 2019 launched an offensive to seize Tripoli from a unity government.

The fighters had been captured near the western city of Zawiya that same month.

On Wednesday, dressed in loose white outfits and matching skullcaps, they were released following a ceremony in Zawiya, 45 kilometres east of Tripoli.

The ceremony took place at a sports ground in Zawiya under heavy security.

In a speech, Abdallah Al Lafi, vice-president of the country's new presidential council, welcomed the move and called for further reconciliation and rebuilding.

"We must not pass on hatred and bitterness to our children," he said.

After a recitation from the Koran and the singing of the national anthem, the prisoners were released and reunited with their families amid loud ululations.

Libya has been ravaged by bloodshed since the fall and killing of leader Muammer Qadhafi in a NATO-backed 2011 revolt.

An array of armed groups arose to fill the vacuum, and many coalesced around the Tripoli-based Government of National Accord (GNA) or around Haftar, who backed an eastern administration.

The two camps, each supported by foreign powers, fought for more than a year before Haftar was forced to retreat.

In October they signed a truce, setting in motion a UN-led process that saw a new transitional government installed in February.

The deal had also led to the release of several dozen prisoners by January.

The new executive is charged with organising national elections set for December 2021.

But while the advances in the peace process have been widely praised, the transitional administration faces a complex task — not least due to the presence of foreign forces who backed the rival camps and have remained on Libyan soil.

Haftar received military support from the UAE and the shadowy Wagner Group, close to the Kremlin, while his rivals were backed by Turkey, whose drones were seen as critical in repelling Haftar’s forces last year.

According to the UN, some 20,000 mercenaries and foreign fighters were still in Libya in early December. A January 23 deadline for their withdrawal passed without any sign of them leaving.

UN Secretary General Antonio Guterres called on the Security Council on Wednesday to give the world body’s UN mission UNSMIL "a clear but flexible mandate, supported by additional resources” to support its ceasefire monitors, who would work alongside Libyan observers from the rival camps.

Both Libyan camps have called for a monitoring mechanism led by Libyans themselves, and Guterres insisted in a December report that "the implementation of the ceasefire agreement must be Libyan-led and Libyan-owned”.

But diplomats have voiced incredulity after the UN’s Libya envoy said last week that as few as five UN officials may be deployed to monitor the truce.

With some 20,000 foreign fighters still in the country, such a mission is a "pretty big task and probably takes more than a few UN ceasefire monitors”, one ambassador to the UN told AFP, asking not to be named.

There also remains the difficult question of crimes committed during the war.

Human Rights Watch has said more than 300 people had been abducted or reported missing in Tarhuna, used by Haftar’s forces as a major staging point for his offensive on Tripoli.

Mass graves were later discovered in the town which was run by the local Al Kani militia.

The rights group’s Libya researcher Hanan Salah tweeted on Wednesday that "No one has been held to account yet for the crimes of abduction, disappearance, torture and unlawful killing of scores of people” in Tarhuna.