Armed clashes erupted on Thursday in Beirut during a protest organised by the Lebanese militant group Hezbollah and its allies against the lead judge probing last year's blast in the city's port.
At least six people were killed and dozens were wounded in the most protracted and violent street fighting in the city in years, authorities said.
The exchanges of fire along a former front line from the 1975-90 civil war involved pistols, automatic rifles and rocket-propelled grenades, and were reminiscent of that conflict.
Gunfire echoed in the Lebanese capital for several hours and ambulances, sirens wailing, rushed to pick up casualties. Snipers shot from buildings. Bullets penetrated apartment windows in the area.
It was not immediately clear what triggered Thursday's violence. Both sides said their protesters came under fire from snipers on rooftops.
Tensions had been running high after the Iran-backed Hezbollah and its Shiite allies from the Amal Movement demanded the removal of Tarek Bitar, the judge leading the investigation into last year's massive port explosion.
The two parties called for a protest near the Justice Palace, located along the former front line between Muslim Shiite and Christian areas.
The violence unfolded while US Undersecretary of State for Political Affairs Victoria Nuland was in town, meeting with Lebanese officials. Her schedule was slightly thrown off by the action on the streets.
Nuland later told an airport news conference that an impartial judiciary is the guarantor of all rights, in apparent criticism of Hezbollah.
The Lebanese people deserve no less and the victims and the families of those lost in the port blast deserve no less, she said. Today's unacceptable violence makes clear what the stakes are.
The demands for Bitar's removal and calls for protests upset many who considered it blatant intervention in the work of the judiciary.
The right wing Christian Lebanese Forces mobilised supporters Wednesday evening after Hezbollah and Amal called for the protest at the Justice Palace, located in a Christian area.
Videos circulating on social media showed supporters of the Christian Lebanese Forces marching in the streets, carrying large crosses.
As the clashes erupted, a journalist with The Associated Press saw a man open fire with a pistol and gunmen shooting in the direction of protesters from the balcony of a building.
Several men fell immediately from the gunfire and bled on the street. The army deployed heavily and sent patrols to the area to search for the gunmen, following the exchanges of gunfire between the Muslim and Christian sides of the capital.
Lebanese authorities said at least six people were killed and 30 wounded. A staffer at the emergency room at al-Sahel hospital said they received three bodies and 15 people who were wounded. One of the dead, a woman, had received a bullet to her head. Two of the injured were in critical condition.
Four projectiles fell near a private French school, Freres of Furn el Chebbak, causing panic, a security official said, speaking on condition of anonymity because he was not authorized to speak to the press.
The students huddled in the central corridors with the windows open to avoid major impact, in scenes reminiscent of the civil war. Smoke covered the neighborhood where intense gunfire was relentless.
A car caught fire, while a blaze was reported in a lower floor where residents were stuck and called for help.
Sporadic shooting continued even after army troops deployed to the area Thursday. Residents and civilians in the area were ducking to avoid the shooting. Someone screamed: Some martyrs on the ground! People pulled one man who was apparently shot and down, away from the line of fire. Others pulled another body away.
In some videos circulating online, some men were chanting: Shiite Shiite on the streets, as residents were running from the gunfire.
In a statement, Prime Minister Najib Mikati appealed for calm and urged people not to be dragged into civil strife.
The court probe centres on hundreds of tons of ammonium nitrates that had been improperly stored at a port warehouse that detonated on August 4, 2020, killing at least 215 people, injuring thousands and destroying parts of nearby neighbourhoods.
It was one of the largest non-nuclear explosions in history and has further devastated the country already roiled by political divisions and unprecedented economic and financial meltdown.
Bitar is the second judge to lead the complicated investigation - his predecessor was removed following legal challenges.
Now Bitar has come up against formidable opposition from the powerful Hezbollah group and its allies who accuse him of singling out politicians for questioning, most of them allied with Hezbollah.
None of Hezbollah's officials have so far been charged in the 14-month-old investigation.
The tensions over the port blast add to Lebanon's enormous multiple troubles, including an unprecedented economic and financial meltdown, an energy crisis leading to extended electricity blackouts, hyperinflation and soaring poverty.
Beirut resident Haneen Chemaly, who heads a local NGOs that provide social services, accused Lebanon's leaders of steering the country into civil war, saying it's the last card they have to use.
They have (driven) us into bankruptcy, devastation and now they are scaring us with the specter of civil war, she said.
Nuland, who said she was visiting to express support for Mikati's new government. At a press conference held at Beirut airport, she urged for strong action by the government that would demonstrate a will to enact reforms.
The armed clash, however, could derail Mikati's month-old government even before it begins tackling Lebanon's economic meltdown.
A Cabinet meeting was cancelled Wednesday after Hezbollah demanded urgent government action against the judge. One Hezbollah-allied minister said he and other Shiite Cabinet members would stage a walkout if Bitar isn't removed, further complicating Mikati's mission.