Protesters remained defiant Monday after supporters of main Shiite groups Hezbollah and Amal attacked demonstrators overnight, sparking a UN call to keep protests peaceful.
Demonstrators demanding a complete government overhaul have stayed mobilised since protests began on October 17, but a bitterly divided political class has yet to find a way forward.
Frustrated by the stalemate, protesters had called for roadblocks and a general strike on Monday, but an attack by supporters of allied parties Hezbollah and Amal on Sunday night weakened the turnout.
Political parties "are trying to instill fear in us as a people, so we don't progress and stay at home," said Dany Ayyash, 21, who was blocking a key road in Beirut's Hamra district.
But "the attack gave us all -- at least the ones here right now -- a sense of determination," Ayyash said.
At around midnight on Sunday, backers of Hezbollah and Amal attacked demonstrators at a flyover near the capital's main protest camp.
Brandishing party flags, they hurled stones at demonstrators and taunted them as riot police deployed to contain the violence.
The attackers also ravaged a nearby encampment, tearing down tents and damaging storefronts in their most serious assault on protesters so far.
At least 10 demonstrators were injured, civil defence said.
On Monday evening, supporters of the two Shiite parties drove by Beirut's Martyrs' Square, where the main protest camp is located, pelting tents with stones before speeding away on motorcyles, an AFP correspondent said.
The UN Security Council called for all actors to maintain "the peaceful character of the protests by avoiding violence and respecting the right to peaceful assembly in protest".
- Tense aftermath -
UN Special Coordinator for Lebanon Jan Kubis earlier called for restraint.
"I urge all Lebanese political forces to control their supporters, to avoid using the national protests for pursuing their political agenda," he tweeted.
The state-run National News Agency said authorities have begun an investigation into Sunday's night incident.
Parliament speaker Nabih Berri, who heads Amal, called on security forces to keep roads open to avoid "civil strife".
On Monday morning, scattered stones, shattered glass and mangled tents littered the camp at Martyrs' Square. Nearby car windows had been smashed with rocks.
Security forces tried to disperse protesters in a neighbouring Beirut district, and removed other demonstrator barricades deployed in the north and east of the country.
The army detained nine people north of Beirut at dawn after they tried to block roads, but freed them later, the military and NNA said.
They also arrested four other "rioters", releasing three shortly afterwards.
The security forces have come under fresh criticism following Sunday's attack, with protesters accusing them of being lax with Hezbollah and Amal supporters, most of whom were allowed to walk away.
"The thugs throw stones and insult security forces but they don't confront them," said Elie, 24, who was among the protesters attacked.
"They don't arrest them the way they arrest us."
Such criticism prompted Interior Minister Raya al-Hasan to say the army and police remain the only "guarantors of the country's stability".
- Political paralysis -
Late Monday, hundreds of Hezbollah and Amal supporters rallied in the capital's Shiite southern suburbs after a man and woman were killed in a car accident earlier the same day.
A video of the incident showed a car ramming at high speed into a metal barrier before catching on fire, in an incident both Shiite parties have blamed on a protester roadblock.
The demonstrators, however, denied any responsibility, publishing a map of their roadblocks on social media.
Political leaders have failed to select a new government nearly a month since Prime Minister Saad Hariri's cabinet resigned under popular pressure.
President Michel Aoun, whose powers include initiating parliamentary consultations to appoint a new premier, said he was open to a government that would include technocrats and representatives of the popular movement -- both key demands of the protesters.
But demonstrators say they reject any government that would also include representatives of established political parties.
The United States, France, the World Bank, and credit rating agencies have all urged officials to accelerate cabinet formation, warning of a deteriorating economic and political crisis.
In the latest diplomatic push, senior British Foreign Office official Richard Moore was in Lebanon on Monday to meet top officials and "underline the urgent need to form a government", the British embassy said.
"The people of Lebanon have been clear in their demand for improved governance, and they should be heard," Moore was quoted as saying.