At least 23 people have been killed since Sunday in Syria-linked clashes between Sunni and Alawite residents of the northern Lebanese port city of Tripoli, a security source said.
Thursday was the bloodiest day yet in the clashes, with at least 11 people killed in 24 hours, the source said on Friday.
Sporadic gunfire was heard on Friday between the neighbourhood of Bab al-Tabbaneh and the hilltop neighbourhood of Jabal Mohsen.
Sunnis sympathetic to Syrian rebels living in Bab al-Tabbaneh have been fighting members of Assad's Alawite sect in Jabal Mohsen.
The fighting on Thursday brought the death toll in the new wave of sectarian violence that started on Sunday to at least 23 people. More than 200 others have been wounded.
Local reports stated the Lebanese army was preparing to move into the two neighbourhoods in an attempt to quell the violence.
In-depth coverage of escalating violence across Syria
Tripoli has suffered intermittent clashes since the Sunni Muslim-led uprising against Syrian President Bashar al-Assad broke out in March 2011, but Wednesday night saw fierce fighting, as the rival sides used mortar bombs, grenade and machineguns.
The two groups have clashed in Tripoli on and off for decades, but the Syrian conflict has reopened old wounds, with each side accusing the other of using the city as a base for sending fighters and weapons in and out of Syria.
Syrian activists said the fighting in Tripoli flared after a fierce assault by Assad's forces on the Syrian border town of Qusayr, where fighters from Lebanon's Hezbollah group are backing government troops in their battle against rebels.
Local politicians said efforts to meet and discuss a ceasefire agreement have so far failed.
Footage of funerals for Hezbollah fighters killed in Qusayr was being watched by Shias across Lebanon, raising
sectarian tensions in other parts of the country, which suffered its own civil war from 1975 to 1990.
In the southern coastal city of Sidon, followers of a radical Sunni religious leader blocked a funeral procession for a Hezbollah fighter.
Lebanese soldiers tried to break the blockade, leading to an exchange of gunfire between the protesters and security forces, residents said. No injuries were reported.