Fighting led to the expulsion of the pro-Assad Arab Movement Party from a largely Sunni Muslim neighborhood in the southern part of Beirut, The New York Times reported.
Three people died and about 20 were injured, Lebanese media reported. Arab Movement Party leader Shaker al-Bijawi said two of the dead were members of his organization.
Bijawi said Sunday he thought the attackers were under orders to assassinate him.
"They have their opinions, we have ours," he told the Times in a telephone interview. "The problem is that they don't want another opinion -- why should we respect their opinion when they don't respect ours -- they keep insulting Syria and Bashar."
The fighting followed the deaths of two anti-Syrian Sunni Muslim clerics at a military checkpoint near Tripoli in northern Lebanon. The area is a hotspot for clashes between a minority Alawite neighborhood and an adjacent Syrian Muslim neighborhood in which nine people died and dozens of people were wounded earlier this month.
Circumstances in which the two clerics died were unclear, the Times said. After an altercation with a soldier at the checkpoint, the two tried to flee in their vehicle and the soldier opened fire, local accounts indicated.
Lebanese Prime Minister Najib Mikati said the army was involved and called for an immediate investigation, saying "appropriate action" would be taken and urged calm. The army expressed regret in a statement.