The most powerful force in the fledgling state, the armed groups remain a law unto themselves. The threat they pose was underscored with the discovery Sunday of at least 53 bodies, people who appeared to have been executed, possibly by anti-Qaddafi fighters.

Peter Bouckaert of Human Rights Watch documented the killings and said the victims, who included Qaddafi loyalists and a senior official in the former government, had been found in the garden of a hotel in Surt. Several had their hands tied behind their backs. The victims were thought to have been killed about a week ago, when the hotel was a base for several former rebel brigades from Misurata, Mr. Bouckaert said.

The discovery came amid continued uncertainty about the circumstances surrounding the deaths of Colonel Qaddafi and his son Muatassim, who may have been killed while in the custody of former rebel fighters. The interim authorities have promised to investigate the deaths.

Libya’s chief forensic pathologist said Sunday that he had performed autopsies on the bodies of Colonel Qaddafi, Muatassim Qaddafi and Abu Bakr Younes, a former defense minister. The pathologist, Dr. Othman al-Zentani, told The Associated Press that Colonel Qaddafi had been killed by a gunshot to the head. Later, he indicated that there may have also been other causes, without providing details.