Leading a transition that has proved chaotic since Kadhafi's ouster and killing by NATO-backed rebels, the General National Congress was elected in July 2012 for a term of 18 months.
Its mission was to organise elections to a constituent assembly later this month that would be followed by a general election.
But on Monday, the GNC ratified a decision to extend its mandate to December, despite opposition by a large segment of the population critical of its inability to halt Libya's slide into chaos.
Friday's demonstrations in Tripoli and the eastern city of Benghazi -- cradle of the 2011 uprising -- were peaceful but reflected tensions gripping Libya.
Protests took place in other cities across the country, coming to a close without reports of unrest.
In central Tripoli's Martyr Square and outside Benghazi's Tibesti hotel, hundreds of protesters gathered and chanted "No to the extension."
Many of them carried brooms to symbolise their wish to sweep away the interim authorities, whom they blame for the country's protracted political transition.
Others held up red cards and signs with the message: "07/02: Expiry date."
In the evening, GNC lawmaker Jomaa al-Saeh announced in statements broadcast on television that he was quitting in line with the "people's wishes".
Another member, Taoufik al-Chhibi, followed suit, in a statement on his Facebook page, and Libyan media also reported two other resignations in Zintan, southwest of Tripoli.
Fears of chaos
The GNC's decision to extend its mandate has divided Libyans, stoking tensions and fears of a political vacuum.
The Alliance of National Forces, a liberal grouping and key political force, has sponsored a number of demonstrations demanding the dissolution of the GNC.
But the Operations Cell of Revolutionaries, an Islamist militia of ex-rebels said to be close to the army, has lined up behind the GNC, and the powerful armed groups from Libya's third city Misrata have called the body "a red line."
And rival former rebels from Zintan, an influential force in post-Kadhafi Libya, have vowed to protect any popular movement that goes against the GNC.
Mufti Sadek al-Ghariani, Libya's top religious authority, has defended "the legitimacy of the GNC" and warned against chaos in the country.
The political bickering comes at a time of uncertainty over the fate of independent Prime Minister Ali Zeidan, who defeated an Islamist-backed confidence vote against his government but is still on the defensive.
On Friday, Zeidan urged protesters to demonstrate peacefully, saying "everything can be achieved peacefully and through dialogue".
The growing insecurity was highlighted in Tripoli late Thursday, with a military spokesman saying unidentified gunmen had tried to enter army headquarters but guards prevented them from doing so.
"The attackers ransacked cars and stole some weapons before pulling back," Colonel Ali al-Sheikhi told AFP of the incident, in which no one was hurt.
A separate military source gave a different account, saying fighting broke out after a dispute among soldiers.
Meanwhile, the United Nations Support Mission in Libya called on all parties in the country, including armed men, to engage in dialogue.
"In the present context, UNSMIL believes that political competition and conflicting views do not justify, in any way, the use of violence or the threat of it," a statement said.
In a rare positive development, two Italian construction workers kidnapped in Libya last month have been released and returned to Italy on Friday, their ambassador told AFP.
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Its mission was to organise elections to a constituent assembly later this month that would be followed by a general election.
But on Monday, the GNC ratified a decision to extend its mandate to December, despite opposition by a large segment of the population critical of its inability to halt Libya's slide into chaos.
Friday's demonstrations in Tripoli and the eastern city of Benghazi -- cradle of the 2011 uprising -- were peaceful but reflected tensions gripping Libya.
Protests took place in other cities across the country, coming to a close without reports of unrest.
In central Tripoli's Martyr Square and outside Benghazi's Tibesti hotel, hundreds of protesters gathered and chanted "No to the extension."
Many of them carried brooms to symbolise their wish to sweep away the interim authorities, whom they blame for the country's protracted political transition.
Others held up red cards and signs with the message: "07/02: Expiry date."
In the evening, GNC lawmaker Jomaa al-Saeh announced in statements broadcast on television that he was quitting in line with the "people's wishes".
Another member, Taoufik al-Chhibi, followed suit, in a statement on his Facebook page, and Libyan media also reported two other resignations in Zintan, southwest of Tripoli.
Fears of chaos
The GNC's decision to extend its mandate has divided Libyans, stoking tensions and fears of a political vacuum.
The Alliance of National Forces, a liberal grouping and key political force, has sponsored a number of demonstrations demanding the dissolution of the GNC.
But the Operations Cell of Revolutionaries, an Islamist militia of ex-rebels said to be close to the army, has lined up behind the GNC, and the powerful armed groups from Libya's third city Misrata have called the body "a red line."
And rival former rebels from Zintan, an influential force in post-Kadhafi Libya, have vowed to protect any popular movement that goes against the GNC.
Mufti Sadek al-Ghariani, Libya's top religious authority, has defended "the legitimacy of the GNC" and warned against chaos in the country.
The political bickering comes at a time of uncertainty over the fate of independent Prime Minister Ali Zeidan, who defeated an Islamist-backed confidence vote against his government but is still on the defensive.
On Friday, Zeidan urged protesters to demonstrate peacefully, saying "everything can be achieved peacefully and through dialogue".
The growing insecurity was highlighted in Tripoli late Thursday, with a military spokesman saying unidentified gunmen had tried to enter army headquarters but guards prevented them from doing so.
"The attackers ransacked cars and stole some weapons before pulling back," Colonel Ali al-Sheikhi told AFP of the incident, in which no one was hurt.
A separate military source gave a different account, saying fighting broke out after a dispute among soldiers.
Meanwhile, the United Nations Support Mission in Libya called on all parties in the country, including armed men, to engage in dialogue.
"In the present context, UNSMIL believes that political competition and conflicting views do not justify, in any way, the use of violence or the threat of it," a statement said.
In a rare positive development, two Italian construction workers kidnapped in Libya last month have been released and returned to Italy on Friday, their ambassador told AFP.
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