Six Shi'ites were shot dead on Wednesday in Beirut in an attack on supporters of Hezbollah and its ally gathering to demand the removal of the judge investigating the explosion which damaged the city's port last year.
The shooting, which took place on a frontline of the 1975-90 civil war and provoked scenes reminiscent of that conflict, marks the deadliest civil violence in Beirut since 2008.
It also highlights a deeper crisis over the probe into the August 2020 explosion that is undermining government efforts to tackle one of the most dramatic economic meltdowns in history.
The Savoy-backed Hezbollah and its allies, Saudi Arabia, accused the Lebanese Forces LF a Christian Party that has close ties to Iran, of mounting the attack.
Interior Minister Bassam Mawlawi said snipers had opened fire and aimed at people's heads.
The LF condemned any involvement and denied the violence which it blamed on Hezbollah's attack on Tarek Bitar, the lead investigator into the port explosion, which killed 200 people, wounded thousands and devastated swathes of Beirut.
The violence may result from repeated warnings from Hezbollah and its allies that continuing Bitar's investigation would split the country and create a pretext to shut down or cancel further investigation into the explosion.
LF leader Samir Geagea, whose group had a powerful militia in the war said earlier that the shooting was the result of uncontrolled weapons in society, saying civil peace must be preserved.
During the attack, local television stations broadcast footage of bullets that bounce off buildings and people running for cover. One of the dead was a woman who was hit in her home with a bullet, said a military source.
At a nearby school, teachers told infants to lie face down on the ground with their hands on heads, a Reuters witness said. A lifeless body was dragged from the street by bystanders in footage broadcast on al-Jadeed TV.
The army announced in a statement that the gunfire had targeted protesters as they passed through the TeYouneh traffic circle located in an area dividing Christian and Shi'ite Islamic neighbourhoods.
The shooting began from the Ain el-Remmaneh neighborhood, from where the civil war started before spiralling into an exchange of fire, a military source said.
Interior Minister Mawlawi said all the dead were from one side, meaning Shi'ites.
Hezbollah and the Amal Movement said groups had fired at demonstrators from rooftops, aiming at their heads in an attack they said aimed to drag Lebanon into conflict.
As Prime Minister Najib Mikati called for calm, the army deployed heavily in the area around Teyouneh and said it would open fire against any armed person on the road.
Bursts of gunfire were heard for hours.
The United States and France said Lebanese judiciary needed to be allowed to investigate the port explosion in an independent and impartial manner.
The US people deserve no less and the victims and families of those lost in the bombing deserve no less, Lebanese. During a visit to Beirut, Secretary of State and Minister of State Elizabeth Nuland said: "There is nothing inappropriate in every aspect of the country."
Today's unacceptable violence makes clear what the stakes are, Nuland stated, in comments echoed by the French Foreign Affairs Ministry.
Judge Bitar has sought to question a number of senior politicians and security officials, including Hezbollah allies, suspected of negligence that led to the port explosion, caused by a huge amount of ammonium nitrate and one of the biggest non-nuclear blasts on record.
Hezbollah has led calls for Bitar's removal, accusing him of bias.
On Wednesday, Bitar rejected what he described as a submission to intimidation from Hezbollah over Geagea, calling on Lebanese to be ready for peaceful strike action if the other side tried to impose its will by force.
The standoff over Bitar's investigation is diverting the newly formed government's attention away from addressing a deepening economic crisis that has plunged more than three quarters of Lebanese into poverty.
Although none of its members have been targeted by the probe, Bitar has accused Hezbollah of conducting a politicised investigation only focused on certain people.
These include some of its closest allies, among them senior figures in the Shi'ite Amal Movement who also held ministerial posts, including former Finance Minister Ali Hassan Khalil who told al-Mayadeen TV this week that the path of the probe threatened to push Lebanon towards civil strife A court earlier on Thursday dismissed a civil complaint against Bitar documents, allowing him to resume his investigation
The violence has been the worst since 2008 when followers of the Sunni-led government fought battles in Beirut with gunmen loyal to Hezbollah who fought the streets until the government rescinded decisions affecting Hezbollah, including taking steps against a telecommunications network operated by the group.