A gunfight broke out during a protest in Beirut on Thursday, killing at least five people and injuring many more.
Exchanges of fire involving snipers, pistols, Kalashnikovs and rocket-propelled grenades marked a dramatic and bloody escalation of tensions over the domestic probe.
The protest outside the Justice Palace was called for by the powerful Hezbollah group which is demanding the removal of Judge Tarek Bitar.
It was not immediately clear what sparked the gunfire, which saw snipers shooting from buildings with bullets penetrating windows.
Students at a nearby French school huddled in the central corridors with the windows open to avoid major impact.
In a statement, Prime Minister Najib Mikati appealed for calm and urged people "not to be dragged into civil strife."
Hundreds of tons of ammonium nitrates that had been improperly stored at a port warehouse detonated on August 4, 2020, killing at least 215 people, injuring thousands and destroying parts of nearby neighborhoods.
Judge Bitar, the second judge to lead the complicated investigation, has come up against formidable opposition from Hezbollah and its allies who accuse him of singling out politicians for questioning, most of them allied with the group.
The shooting continued even after army troops deployed to the area with the sound of exchange of fire ringing over their heads.
Residents and civilians in the area were ducking to avoid the shooting, some screaming: “Some martyrs on the ground!”
The army then began firing at the crowd. The streets quickly became deserted, with only sounds of bullets, as shops were shut down.