"One of the rebel leaders confirmed to me that Khamis was killed somewhere near Tarhuna, about 80 kilometres (50 miles) south of Tripoli," the opposition justice and human rights minister Mohammed al-Allagy told AFP.
"He may have been killed in battle. The rebel leader said he had been buried," Allagy added.
Rebel government spokesman Mahmud Shammam backed the report, telling a press conference that Khamis had been killed between Tarhuna and Zliten.
"Khamis was killed, a leader of the revolution in that region told me so. (...) I haven't seen the photos of the body but that leader told me and I believe him," Shammam said.
The rebels said on Sunday that Khamis may have been killed the day before in a clash between their fighters and pro-Gaddafi forces.
Rebel military spokesman Ahmed Omar Bani said Saturday that Khamis could have been one of several people killed when rebel fighters in Tarhuna intercepted a military convoy with several "brand new Mercedes vehicles".
"As our fighters were trying to block the passing of the convoy, they were violently attacked and shot at," said Bani.
"The brigade in Tarhuna responded and hit two vehicles in the convoy, killing their occupants."
"We faced strong resistance (from the pro-Gaddafi convoy) to protect these two cars which is why they were totally destroyed and burned with their occupants caught in the crossfire," he told reporters in Benghazi.