At least 50 charred bodies were found in a hanger. Gadhafi loyalists are accused of opening fire and tossing grenades at 150 civilians in the hangar after promising to release them.
Libyan rebel leaders asked NATO on Monday to keep up pressure on elements of Gadhafi's regime and to protect those struggling to restore electricity and water to the battle-scarred capital of Tripoli.
Despite effectively ending his rule, the rebels have yet to find Gadhafi or his family members- something that has cast a pall of lingering uncertainty over the opposition's victory.
NATO has been bombing Gadhafi's forces since March under a United Nations mandate to protect Libyan civilians.
Rebels appear to have secured the capital after a week of fierce fighting in which they captured Gadhafi's compound and then cleared loyalists holed up in the residential neighborhood of Abu Salim nearby.
Outside Tripoli, Gadhafi's hometown of Sirte is still a bastion of support and some have even speculated that the ousted leader himself may have fled there. Rebels have been converging from the east and west on Sirte, 250 miles east of Tripoli, preparing to battle Gadhafi loyalists.
No fighting in Sirte itself has been reported yet and rebel leaders say they are trying to negotiate a peaceful surrender with local tribes to avoid further bloodshed.
Rebels say they want to take Gadhafi alive so they can try him in Libya.
Meantime, the man convicted in the 1988 Lockerbie bombing in Tripoli has been tracked down. His family says he's in a coma and near death and should not be returned to prison.
New York senators on Aug. 22 asked the Libyan rebels' transitional government to hold al-Megrahi fully accountable for the 1988 bombing of Pan Am flight 103, which killed 270 people. Rebel leaders have said they will not extradite him.
The Scottish government released Abdel Baset al-Megrahi in 2009, believing he would soon die of cancer. He was greeted as a hero in Libya.
The Associated Press contributed to this story.