Seven bodies were found buried in the grave that was discovered in a farm west of the city, while three prisoners were saved when security forces came across a secret prison in another town after liberating it from the militants, Alaraby reported.
The prisoners, said to be held captive for several months, were found in dire humanitarian conditions, the anonymous source said.
Meanwhile, the battle to cleanse Sirte of ISIL and Daesh militants has continued to progress with government forces closing in on the group’s stronghold.
Last week, fighters allied to the Government of National Accord encircled ISIL and Daesh in the Ouagadougou conference center, a huge building the group has made as its headquarters.
“Fighting is ongoing around the presidential palaces close to the port and at the Ouagadougou conference center,” the spokesman for the anti-ISIL and Daesh operation, Mohammad al-Ghasry said.
“Ground troops are working in conjunction with snipers, while artillery and the air force are bombarding the conference center and the neighboring district. We have almost taken back the whole of Sirte,” he added.
ISIL overran the city, around 450 kilometers East of the capital Tripoli, in June last year.
Nearly 200 anti-ISIL fighters have been killed and more than 600 wounded since the start of the offensive, according to medical sources.
Pro-government forces, commanded out of Misrata 190 kilometers to the Northwest, are mostly made up of Western militias established during the 2011 revolt that overthrew dictator Muammar Gaddafi.