|The ICC is seeking the arrest of Saif al-Islam along with other Libyan officials for alleged war crimes [EPA]
Libya's Muammar Gaddafi is willing to hold elections and step aside if he lost, his son has said, an offer quickly dismissed on Thursday by rebels and US officials.
The rebel leadership in the eastern stronghold of Benghazi described the offer as "wasting our time".
"Saif al-Islam is not in a position to offer elections. Libya will have free elections and democracy but the Gaddafi family has no role to play in this process," Jalal el-Gallal, a rebel spokesman, told Reuters.
"These people are criminals, they have utter disregard for human life. They have to withdraw troops from our cities, allow humanitarian aid to reach people, they will face justice for their crimes. Only then we can talk about holding elections."
Saif al-Islam's proposal, which follows a string of concessions offered by Gaddafi that Western powers have dismissed as ploys, came amid mounting frustration from some NATO members at the progress of the military campaign.
"They (elections) could be held within three months. At the maximum by the end of the year, and the guarantee of transparency could be the presence of international observers," Saif al-Islam told Italian newspaper Corriere della Sera.
He said his father, who has ruled the country for more than four decades, would be ready to step aside if he lost the election but would not go into exile.
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"I have no doubt that the overwhelming majority of Libyans stand with my father and sees the rebels as fanatical Islamist fundamentalists, terrorists stirred up from abroad," the newspaper quoted Saif al-Islam as saying.
It was not clear what form the proposed vote would take. Libya has never held elections under Gaddafi and has no elected institutions.
Victoria Nuland, a US state department spokesperson, told reporters at Thursday's daily briefing, "I think it's a little late for that", and repeated the US view that "it's time for [Gaddafi] to go".
Saif al-Islam is among three top Libyan officials wanted by the International Criminal Court for alleged war crimes committed by Gaddafi's regime in bid to quell an uprising against his rule.
He made the offer as Libyan officials ruled out Gaddafi's departure during talks with Mikhail Margelov, the envoy leading Russia's efforts to end the Libyan conflict.
Al-Baghdadi Ali Al-Mahmoudi, Libya's prime minister, put the potential concession in question, telling reporters: "I would like to correct [that] and say that the leader of the revolution is not concerned by any referendum".
Al-Mahmoudi said that there was no reason for the Libyan leader to step down in any case, because he had not held any formal political or administrative post since 1977.
Amid the political standoff, explosions continued to rock Tripoli with fresh NATO air strikes reported on Thursday morning.
NATO warplanes have repeatedly targeted the area in and around the Bab al-Aziziya compound, Gaddafi's command centre.
The North Atlantic alliance launched its air campaign nearly three months ago under a UN resolution to protect civilians after Gaddafi's troops used force to put down the rebellion against his rule in February.
The Libyan leader has described the rebels as "rats" and says NATO's campaign is an act of colonial aggression aimed at stealing Libya's oil.
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Rebel forces are now fighting Gaddafi's troops on three fronts: in the east of the country around the oil town of Brega; on the edge of rebel-held Misurata, Libya's third-biggest city; and in the western mountains south-west of Tripoli.
Rebels in the western mountains said on Wednesday they had taken control of two villages from pro-Gaddafi forces, building on gains which in the past few days have seen them advance to within about 100km of Tripoli.
But rebel forces show no signs of being able to break through to the capital soon.