At least six people were killed in Beirut on Thursday when heavy gunfire targeted supporters of Hezbollah, as they headed to a protest demanding the removal of the judge investigating last year's explosion at the city's port.
The shooting on a frontline of the 1975-90 civil war marks some of Lebanon's worst civil strife in years, and highlights a deepening political crisis over the probe into the catastrophic August 4, 2020 blast.
The Lebanese army said in a statement the gunfire had targeted protesters as they passed through a traffic circle located in an area dividing Christian and Muslim neighbourhoods.
Bursts of gunfire were heard for several hours, along with several explosions which appeared to be rocket-propelled grenades fired into the air, Reuters witnesses said.
Lebanon's army said later on Thursday it arrested nine people, including a Syrian, in connection with the violence.
Prime Minister Najib Mikati announced on Twitter that Friday would be a day of public mourning for the lives of those killed.
Political tensions over the probe into the 2020 Beirut port explosion have been building, with the heavily armed, Iran-backed Hezbollah leading calls for Bitar's removal, accusing him of bias.
The explosion killed more than 200 people and devastated swathes of Beirut.
The standoff over Bitar's investigation is diverting the newly formed government's attention away from tackling one of the worst economic meltdowns in history.
The judge has sought to question a number of senior politicians and security officials, including Hezbollah allies, suspected of negligence that led to the port explosion, which was caused by a huge quantity of ammonium nitrate.
All have denied wrongdoing.
Though none of its members have been targeted by the probe, the heavily armed Hezbollah has accused Bitar of conducting a politicised probe only focused on certain people.
These include some of its closest allies, among them senior figures in the Amal Movement who occupied ministerial posts.
A court earlier on Thursday dismissed a legal complaint against the Bitar, documents showed - allowing him to resume his investigation.
On Wednesday, Samir Geagea, a Christian opponent of Hezbollah, rejected what he described as any submission to "intimidation" by the group, calling on Lebanese to be ready for peaceful strike action if the "other side" tried to impose its will by force.