Rebel-held prisoners of war have told of the difficulties their units are increasingly facing, as Human Rights Watch (HRW) accused rebel forces of human rights abuses.
The ex-government troops told CNN of shortages of food, fuel and ammunition.
More than 100 are being held by rebels in one school.
Libyan rebel forces, HRW alleged, have been responsible for looting, arson and the abuse of civilians in their push toward Tripoli.
The group said it "witnessed some of these acts, interviewed witnesses to others, and spoke with a rebel commander about the abuses."
The abuses were said to have taken place in June and July - as recently as last week - as rebel forces pushed through the Nafusa Mountains to the south of Tripoli.
"In four towns captured by rebels in the Nafusa Mountains over the past month, rebel fighters and supporters have damaged property, burned some homes, looted from hospitals, homes, and shops, and beaten some individuals alleged to have supported government forces," said HRW.
POLITICAL SOLUTION
Meanwhile, French and Libyan officials are talking up the chances of negotiating Muammar Gaddafi's withdrawal from power and an end to the conflict wracking his country, after months of military stalemate.
Gaddafi's prime minister told a French daily on Tuesday the embattled regime was ready to begin talks with Paris and Libyan rebels "without preconditions" and without the interference of its authoritarian "Guide".
France - which has spearheaded the Western diplomatic and military response to the crisis -- confirmed it is in indirect talks to bring the fighting to an end and to smooth Gaddafi's departure.
"A political solution in Libya is more vital than ever and it is beginning to take shape," Prime Minister Francois Fillon told MPs
