Libyans angered by rising prices, chronic power cuts and political deadlock planned further protests on Monday after a night of angry demonstrations across the capital.
Masked youths set car tyres alight and blocked roads, including a major coastal highway between central Tripoli and its western suburbs, but security forces did not intervene.
Videos carried by local media also showed demonstrations in Beni Walid and the port city of Misrata.
A youth movement calling itself Beltress said further protests were planned in Tripoli's Martyrs' Square at 4pm local time.
The movement is calling for elections and the dissolution of both the country's rival governments and their two houses of parliament.
Public anger has been fuelled by power cuts that often last 18 hours amid soaring summer temperatures, despite Libya sitting on Africa's largest oil reserves.
The vast country has been mired in political unrest and armed violence since a 2011 Nato-backed uprising toppled and killed dictator Muammar Qaddafi.
On Friday night, protesters stormed the seat of the House of Representatives in the eastern city of Tobruk, ransacking its offices and torching part of the building.
In both Tripoli and the main eastern city of Benghazi, the cradle of the 2011 uprising, thousands took to the streets to chants of “We want the lights to work”.
Some brandished the green flags of the former Qaddafi regime.
United Nations Secretary General Antonio Guterres has called for calm, but UN-mediated talks in Geneva last week aimed at breaking the stalemate between rival Libyan institutions failed to resolve key differences.
Presidential and parliamentary elections, originally set for last December, were meant to cap a UN-led peace process following the end of the last major round of violence in 2020.
But voting never took place due to several contentious candidacies and deep disagreements over the polls' legal basis between the rival power centres in east and west.
The crisis deepened this year as parliament, elected in 2014 and backed by eastern military commander Khalifa Haftar, appointed a new government to replace that of interim leader Abdul Hamid Dbeibah.
He has refused to cede power except to an elected administration.
On top of the political deadlock, Libyans' living standards have been hit hard by price rises on food imports due to the war in Ukraine.
Also, supporters of the rival administration of former interior minister Fathi Bashagha have shut down several oil facilities since April as leverage in his power struggle with Mr Dbeibah.
Libya expert Jalel Harchaoui told AFP that “kleptocracy and systematic corruption” were rife in both eastern and western Libya.
For normal Libyans the year “has been extremely painful” because the country “imports almost all its food and the Ukraine war has hit consumer prices”, Mr Harchaoui said.
Meanwhile, a UN-appointed mission to Libya said on Monday there are “probable mass graves” yet to be investigated, possibly as many as 100, in a town where hundreds of bodies have already been found, and it urged Tripoli to keep searching.
The report to be submitted to the UN Human Rights Council this week details how a militia run by seven brothers executed and imprisoned hundreds of people between 2016-2020, sometimes keeping them in tiny oven-like structures called “the boxes” which were set alight during interrogations.
Evidence of kidnappings, murder and torture in Tarhouna, uncovered by the independent Fact-Finding Mission (FFM), represents one of the most egregious examples of rights abuses in the turbulent period since Qaddafi's removal in 2011.
Among the victims were disabled people, women and children, the 51-page report said.
Based on the testimonies of residents and two site visits, the FFM found “reasonable grounds” that the Kaniyat militia committed crimes against humanity. It identified four commanders who participated directly in them.
Libyan authorities have already recovered 247 bodies in mass and individual grave sites in the Tarhouna area in western Libya. Many were still handcuffed and blindfolded.
The mission used satellite imagery showing signs of soil disturbances among other evidence to identify three new likely sites. But there could be many more, it said, citing an existing grave known as “The Landfill” where just a tiny fraction of the site has been investigated.
“According to insider knowledge, there might still be up to 100 as of yet undiscovered mass graves,” the report said.
It is not immediately clear how the findings will reflect on Libyan authorities. Libya's diplomatic mission in Geneva did not respond to a request for comment.
At one stage, the Kaniyat was aligned with the Tripoli-based Government of National Accord but later with the eastern Libyan National Army led by Mr Haftar that tried, unsuccessfully, to overthrow the National Accord administration. The militia no longer holds authority in Tarhouna.
The surviving leaders of the Kaniyat are mostly believed to have fled to areas of eastern Libya under Mr Haftar's control.
In its conclusions, the FFM called on Libyan authorities to continue searching for the graves. It also urged them to establish a special tribunal to prosecute international crimes.
Tracy Robinson, one of the three heads in charge of the 18-person team, said it did not have the resources or authority to investigate the Tarhouna graves alone. “It's the state's duty to act,” she told journalists in Geneva.
The report refers to difficulties with co-operation with Libyan authorities in the past. Diplomats and UN sources also told Reuters that Libya had previously expressed reservations about continuing the mission, which expires this month.
A resolution is currently before the Geneva-based council to keep investigations going for another nine months, which is less than some had hoped for.
A decision is expected this week and, if successful, FFM members said they intend to submit further evidence, a final report and a confidential list of individual suspects to the council next year.