The first mass grave with 19 bodies was found on Friday on a farm in the southeastern city of Kufra, according to a Libyan security authority in a statement, adding that the bodies have been taken away for autopsy.
The charity organization al-Abreen, which helps migrants in eastern and southern Libya, reports that some of them were shot before being buried.
Another mass grave with at least 30 bodies was also found in Kufra after a raid on a human trafficking center. Survivors report that nearly 70 people were buried in the grave, according to Libyan authorities who are still searching the area.
Mass graves with migrants are not uncommon in Libya. Last year, authorities dug up the bodies of at least 65 people in the Shuayrif region, about 35 miles south of the capital Tripoli.
