Three people died and 23 were wounded during fierce clashes on Saturday between Lebanese Sunni Muslims hostile to Syria's regime and Alawites who support it, a Lebanese security official said.
"A Sunni and an Alawite were killed and 23 people were wounded in clashes that continued since Friday between people from the neighbourhoods of Jabal Mohsen and Bab al-Tebbaneh" in the northern city of Tripoli, the official told AFP.
A 17-year-old girl died of her wounds later.
Ten soldiers were among those wounded in the fighting, among them a sergeant whose wounds were critical, the official added.
The two sides fired guns and rocket-propelled grenades at each other in the bloodiest clashes since last June when six people were killed in the wake of demonstrations against the Syrian government.
Sunni-majority Tripoli has in the past few years been the scene of intense clashes between Sunni supporters of the anti-Syrian opposition and Alawite Muslims loyal to a Hezbollah-led alliance backed by Iran and Syria.
Syrian President Bashar al-Assad, who is fighting an unprecedented revolt against his regime, is from the Alawite community, an offshoot of Shiite Islam.
The Lebanese army is deployed on the outskirts of Jabal Mohsen and Bab al-Tebbaneh, namely near Syria Street which separates the rival neighbourhoods.
Some residents have fled the area while those who stayed behind -- both Sunnis and Alawites -- said they are afraid that clashes will erupt anew while blaming the other side for the fighting.
"I am paying the price of a war which is not mine," said Zeinab Yaghi, a 55-year-old Sunni Muslim mother of five whose house was hit in the crossfire.
"I know nothing about politics but supporters of the Damascus regime are causing problems here," she said after fleeing her home with her children.
One Sunni man who declined to be identified said "rockets have been raining down on us since yesterday (Friday)."
"They are constantly provoking us and waving pictures of Bashar al-Assad," he said of his Alawite neighbours, adding however that he was not against the Alawites.
Some Alawites also expressed concern, saying they were afraid for their lives.
"We are afraid because there is a sectarian spin to things," said Khaled al-Ali, a taxi driver.
"Since the crisis began in Syria we have been treated like foreigners. They provoke us all day long by staging anti-Alawite rallies," he said.
"The imams in the mosques are setting the (Sunnis) against us in their sermons and we constantly receive threats saying we would be expelled from Tripoli if the regime in Syria falls," he added.
The fighting erupted on Friday but subsided by Saturday afternoon after the army negotiated a truce between the two communities, officials said.
"I could not care less what happens in Syria," said Mohammed Khaldiye, an Alawite.
"I just want to live in peace with my neighbours, in my city" of Tripoli.