A mass grave containing "at least 65 migrants' bodies" was discovered in southwest Libya this week, the UN migration agency said Friday.

A spokesman for the International Organization for Migration told AFP the mass grave was unocovered by Libyan security forces.

The IOM said it was "profoundly shocked and alarmed". It added that the circumstances of the deaths "remains unknown".

"But it is believed that they died in the process of being smuggled through the desert," the agency said in a statement.

More than a decade of violent instability since the 2011 overthrow and killing of dictator Moamer Kadhafi in a NATO-backed uprising helped turn Libya into a fertile ground for human traffickers, who have long been accused of abuses against migrants.

The IOM said it appreciated that Libyan authorities had launched an investigation into the deaths. It called on them to "ensure a dignified recovery, identification and transfer of the remains of the deceased migrants", and notify and assist their families.

"Each report of a missing migrant or a loss of life represents a grieving family searching for answers about their loved ones or acknowledging the tragedy of the loss," a spokesperson said in the statement.

"The cost of inadequate action is evident in the increasing human deaths and the disturbing conditions migrants find themselves in."

The IOM said the deaths showed "the urgent need to address the challenges of irregular migration including through a coordinated response to the smuggling of migrants and trafficking in persons".

"Without regular pathways that provide opportunities for legal migration, such tragedies will continue to be a feature along this route," it said.

According to the IOM's Missing Migrants Project, at least 3,129 deaths and disappearances were recorded in 2023 along the Mediterranean route to Europe, making it the world's deadliest migratory route.

The IOM called on authorities in countries along the route to "enhance regional cooperation to ensure the safety and protection of migrants, regardless of their status, and across all stages of their journeys".