Libyan security authorities have recovered at least 11 more bodies of migrants from a mass grave in the southeast of the country, a security official told Reuters on Thursday.

The total number of bodies recovered, found in 55 graves, has now climbed to 39 after the attorney general said on Sunday that the authorities had recovered the corpses of 28 others in the north of Kufra, a huge southeastern district of the country.

The International Organization for Migration said on Monday that the bodies found in two mass graves in Libya bore gunshot wounds.

The main town in Kufra lies about 1,700 kilometres (1,000 miles) from the capital Tripoli.

"We expect to find other graves during the ongoing recovering operation," said Mohamed Fadil, the head of services fighting illegal migration in the largely desert region.

Fadil said the bodies had been numbered and samples for DNA testing taken in the presence of prosecutors and the criminal investigation department.

Pictures shared with Reuters by a security source from Kufra showed security authorities and Libyan Red Crescent volunteers had set up tents in the desert, with white lines visible on the ground marking out the graves.

Libya has become a transit route for migrants fleeing conflict and poverty to Europe via dangerous routes across the vast Sahara desert and over the Mediterranean, following the toppling of Muammar Gaddafi in a NATO-backed uprising in 2011.

On February 6, the security directorate in the Alwahat region in the east of Libya recovered 19 bodies from a mass grave in Jikharra, while the Libyan Red Crescent recovered 10 bodies of migrants off Dila port in Zawiya city in the west after their boat sank.