Former Libyan justice minister Mustafa Abdel Jalil said the opposition had rejected Gaddafi's plea to negotiate a settlement because they did not trust former prime minister and Gaddafi loyalist Jadallah Azzouz Talhi.
Libya remained tense Tuesday with fighting raging in some towns between forces loyal to Gaddafi and the opposition which has gained the support of the West.
The unrest that broke out Feb 14 has so far claimed, according to one estimate, 6,000 people dead. Another 140,000, mainly foreigners, have fled the country.
The opposition wants Gaddafi, who has ruled Libya since 1969, to go.
Saadi Gaddafi, son of the Libyan leader, warned that Gaddafi's exit, if it came out, would not mirror Egyptian leader Hosni Mubarak's.
"The tribes are all armed, there are forces from the Libyan army and the eastern region is armed. The situation is not like Tunisia or Egypt," he told Al Arabiya television channel.
"The situation is very dangerous. From the perspective of a civil war, the leader must play a very, very big role in calming Libya and convincing people to sit together. If something happened to the leader, who would be in control? A civil war would start."
Fierce fighting raged in towns under rebel control.
A rebel group claimed Tuesday that an undetermined number of Libyan army officers were killed for refusing to fire at anti-government protesters in a mountainous region west of Tripoli, Al Jazeera reported.
Libyan state media said the army retook a rebel base in the western city of Az Zawiya.
However, the opposition regrouped in towns in the east. The military has for now apparently halted the rebel advance to the Libyan leader's hometown Sirte.
Former minister Jalil, also chairman of the rebel National Libyan Council, told Al Arabiya: "We refused to negotiate with Muammar Gaddafi because we didn't trust the mediator that contacted us."
Gaddafi had reportedly sought to negotiate a safe departure for himself and his family.
He proposed a meeting of parliament to agree a transition period to pave the way for him to leave. He also wants immunity from criminal prosecution and permission to take away a large amount of cash.
Jalil said the opposition would consider not seeking prosecution through the International Court of Justice if Gaddafi left the country.
"If Gaddafi gave up power, we could decide not to pursue him on an international level. We want him to step down first, and only then can we have talks," he said.
NATO Secretary General Anders Fogh Rasmussen meanwhile warned that the world would not allow the Gaddafi regime to continue attacking opposition forces.
The US said it was considering giving weapons to Libyan rebels.
"On the issue of arming, providing weapons, it is one of the range of options that is being considered," White House spokesman Jay Carney said.
The US was reaching out to the opposition in Libya to ensure they were committed to building a democratic government respectful of human rights, Carney said.