BEIRUT: At least two people were killed in Beirut on Thursday when heavy gunfire targeted supporters of the Lebanese Shi'ite group 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 Aug. 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 Shi'ite Muslim neighbourhoods.

As Prime Minister Najib Mikati called for calm, a military source told Reuters two people had been killed and seven more wounded.

The shooting began from the Christian neighborhood of Ain el-Remmaneh before spiralling into an exchange of fire, the source added.

Hezbollah's al-Manar TV said "two martyrs" and a number of wounded had been taken to a hospital in the Shi'ite southern suburbs, indicating that the casualties were Shi'ites.

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.

The Lebanese army deployed heavily in the area and said it would open fire against any armed person on the road.

Political tensions over the probe into the 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 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, Iran-backed 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 Shi'ite 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.