Colonel Muammar Gaddafi was last seen heading south of Tripoli after holding meetings in the capital on Friday, the bodyguard of one of his sons tells Sky News.
The 17-year-old - part of Khamis Gaddafi's protection team - told Sky's chief correspondent Stuart Ramsay he saw the former dictator at his youngest son's compound at the end of last week.
Col Gaddafi arrived in a car and met Khamis and his daughter Aisha before heading in convoy towards Sabha, said the bodyguard Abdu Salam Ataher-Ali.
He also confirmed earlier reports by rebel commanders that Khamis had been killed in an air strike about 37 miles (60km) from Tripoli.
Ramsay said the bodyguard claimed Khamis died when his armoured Toyota Land Cruiser was hit by a missile, which was apparently launched from a Nato helicopter.
Nato says it has "no information" on Col Gaddafi's son.
Khamis, who has been reported dead on a number of occasions during the six-month uprising, is one of the most feared members of the regime.
He was the commander of the country's elite special forces, known as the 32nd brigade.
As the hunt for Col Gaddafi continues, other family members are confirmed to have been given refuge in neighbouring Algeria.
Algeria's foreign ministry said the former Libyan leader's wife Safia, daughter Aisha and sons Hannibal and Mohammed all entered the country on Monday morning.
A health ministry official said Ayesha has given birth to a baby girl since arriving in the country.
A ministry spokesman insisted the four had been allowed into the country "for strictly humanitarian reasons".
"We have informed the Secretary General of the United Nations, the president of the (UN) Security Council and the president of the executive council of the NTC," Amar Belani said.
Libya's National Transitional Council (NTC) reacted angrily to the news, with its chairman Mustafa Abdel Jalil calling on the Algerian government to hand over any of the Gaddafi family members who are wanted for trial.
NTC spokesman Mahmoud Shamman said: "We have promised to provide a just trial to all those criminals and therefore we consider this an act of aggression.
"We are warning anybody not to shelter Gaddafi and his sons. We are going after them... to find them and arrest them."
He added: "We have heard that Algeria will harbour them until they go to another country. They are trying to go to another country, possibly an east European country."
The dispute could lead to a diplomatic rift between the NTC and one of its neighbours as it tries to gain recognition as Libya's government.
So far, Algeria has not recognised the NTC and has adopted a stance of strict neutrality on the Libyan conflict, leading some rebels to accuse it of supporting the Gaddafi regime.
Britain has reiterated its support for the NTC's efforts to make sure Col Gaddafi faces justice.
Anti-Gaddafi forces are advancing on Sirte from two sides
:: Who's Who In Gaddafi's Inner Circle
Despite the emergence of some of his family members, the whereabouts of Col Gaddafi and his most prominent son Saif al Islam are still unknown.
There has been speculation that the colonel has fled to his home town of Sirte.
Anti-Gaddafi forces are advancing on the town from both the east and west and Nato planes have hit targets there.
Talks are ongoing to secure the surrender of the town but troops say they are prepared to take Sirte by force if necessary.
Nato has said the country's warring sides are engaged in "discussions" in the loyalist stronghold.