At least six people were wounded when clashes erupted in the capital Beirut Sunday night after Lebanese army soldiers shot dead a Sunni Muslim cleric, a Lebanese security source told dpa.
The cleric, Ahmed Abdel Wahed, was known for his backing the uprising against Syrian President Bashar al-Assad. His aide was also killed in the incident in the northern region of Koueikhat, his supporters said.
A witness in the area of the clashes told dpa that rocket-propelled grenades and heavy machine guns were being used in the street battles that left the city like a ghost town.
The clashes occurred in the neighborhood of Tarek Jadidah, inside the capital Beirut. They pitted two Sunni factions against each other - one that opposes Syria's president al-Assad against another that is loyal to a Sunni political figure, Shaker Berjawi, who supports the Syrian president, the source said.
The ongoing violence in Tripoli between supporters and opponents of the Syrian regime has raised fears that the conflict in Syria will spill over to Lebanon.
After the killing, angry protesters used burning tyres to block roads in the capital and northern and eastern Lebanon. Lebanese Army troops backed by tanks were seen deploying in tense neighbourhoods inside the capital, to prevent any further escalation of the situation.
The military said that it was investigating the lethal incident involving the cleric, which occurred at an army checkpoint near the port city of Tripoli, where Sunni Muslims last week fought deadly clashes with Alawite supporters of al-Assad that left at least 10 people dead.
Al-Assad is a member of the Alawite sect, an offshoot of Shia Islam.
"The leadership of the army expresses deep regret for the death of the two victims ... It will immediately form an investigative committee comprised of senior officers and military police," the army said in a statement said.
Prime Minister Najib Mikati in a statement said that the government was "determined" to carry out its national duties "amid this critical period in Lebanon and the region."
The Syrian crisis has divided Lebanon between the Western and Arab-backed opposition and the powerful Shiite movement Hezbollah, which dominates the Lebanese government and is allied with Syria and Iran.