Sectarian clashes linked to the 21-month conflict in Syria killed four people and wounded 40 in neighbouring Lebanon before dawn on Sunday, a security official said.
The latest fighting in the northern city of Tripoli between Sunni Muslims and Alawite co-religionists of Syrian President Bashar al-Assad came amid growing international concern about the potential for neighbouring countries to be dragged into the conflict.
Sunni residents of the port city's Bab al-Tebbaneh district exchanged machinegun and rocket fire with Alawite residents of the neighbouring Jabal Mohsen district leaving two members of each community dead, the security official said.
The fighting broke a tense calm that had held since the army deployed troops between the two impoverished neighbourhoods early on Friday.
During the night, troops held their positions on sidestreets but not on the ironically named Syria Street that forms the frontline.
"The clashes are light now," the official said on Sunday morning, adding that no decision had yet been taken on whether to send in more troops.
The latest deaths brought the toll from fighting in the city since Tuesday to 17, including two children.
Longstanding tensions in Tripoli escalated in mid-week when 22 Sunnis from the city who had crossed into Syria to join the armed rebellion against Assad's rule were killed in an ambush by troops.
Damascus later agreed to repatriate the bodies, and on Sunday three of the slain fighters were received at the Lebanese border, a security source said.