Fresh clashes erupted in Tripoli Saturday as the death toll from a shootout at an anti-militia protest rose to 43 and the weak, post-revolutionary government appealed for restraint.
More than 450 people were wounded when Friday's protest sparked clashes in the capital between militias that continued overnight, Justice Minister Salah al-Marghani said.
Prime Minister Ali Zeidan, who was briefly abducted by militiamen last month in an incident that underscored growing instability, appealed for "restraint and a halt to the clashes," warning that "the coming hours and days will be decisive for the history of Libya".
Late Saturday, local authorities in Tripoli announced a "three-day general strike in all public and private sectors starting Sunday" in response to the violence.
The country has seen a surge in unrest as former rebels who helped topple Moamer Kadhafi's decades-old regime in 2011 have scoffed at government demands to lay down their arms.
The latest violence erupted when protesters carrying white flags marched on a cluster of villas that serve as the Tripoli base of the Misrata brigade -- made up of battle-hardened fighters from the western city of the same name -- and demanded they leave the capital.
Gunmen opened fire from inside the villas at Gharghour, killing several protesters and prompting rival militias to attack the base, setting part of it ablaze.
The coastal city of Misrata, 200 kilometres (120 miles) east of Tripoli, saw some of the 2011 uprising's fiercest fighting.
The Misrata brigade attacked an army barracks early Saturday, igniting another round of clashes in which one person was killed and eight wounded, according to Colonel Mosbah al-Harna, commander of another brigade nominally under the authority of the defence ministry.
Harna said the Misrata militiamen then looted the base, taking away vehicles, weapons and ammunition.
More fighters from Misrata tried to enter Tripoli from the east, sparking clashes with rival militias before the column of reinforcements pulled back several kilometres.
The "Shield of Libya", another former rebel brigade formally under government control, later announced that it had secured Gharghour as the Misrata fighters withdrew.
A "Shield of Libya" brigade in the restive eastern city of Benghazi was itself the target of a protest in June that also turned bloody, with more than 30 people killed.
The road into Tripoli from the east was meanwhile closed off, an AFP journalist said, and the city was quiet on Saturday evening, with many businesses and shops closed.
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'An insult to the memory of the martyrs'
Secretary of State John Kerry said the United States -- which had contributed to a NATO air campaign in support of the rebels two years ago -- was "deeply concerned" about the clashes, and urged all sides to "exercise restraint and restore calm".
Earlier in the day, US ambassador Deborah Jones tweeted that it was "heartbreaking to hear continuing gunfire. An insult to the memory of the martyrs."
The UN mission in Tripoli also condemned the violence, urging Libyans to use "peaceful means to resolve their differences".
Zeidan initially said armed demonstrators were involved in Friday's clashes and security forces had not intervened "so as not to complicate the situation".
But he later backtracked to say the protest march had been "peaceful" and came under fire when it entered Gharghour.
Last week Zeidan had urged Libyans to rebel against militias, saying: "The people must take to the streets... and support the building up of the army and police."
In sermons at midday Muslim prayers on Friday, imams had backed the calls for protests.
Sadat al-Badri, president of Tripoli city council, which had called Friday's protest, insisted the demonstrators were unarmed.
Gunmen inside the Misrata base initially fired into the air to try to scare off the protesters -- who had children with them -- but when the demonstrators kept advancing the militiamen shot into the crowd, an AFP correspondent said.
A Misrata commander told private television channel Al-Naba that demonstrators had opened fire first.
The march was a response to heavy clashes on November 7 between the Misrata brigade and a rival militia.
Hundreds of people gathered in Tripoli's Martyrs' Square on Saturday for the funerals of three of those killed in Friday's clashes, chanting slogans against the militias.
The rebels who overthrew Kadhafi were hailed as heroes after ending his 40-year dictatorship, but many have since carved out their own fiefdoms and been accused of mafia-like extortion and other crimes.