"Civil war can start in Tripoli and later spread out in Lebanon," Rifaat Eid, a leader from the pro-Syrian Arab Democratic Party, was quoted as saying by The Daily Star newspaper in Lebanon.
Party leaders this week were charged with helping coordinate August bombings in Tripoli said to be the work of Syrian intelligence officials.
The ADP leader said the government in Beirut was ignoring the plight of Alawites, a Shiite sect, because of pressure from Sunni leaders in Saudi Arabia.
Syrian President Bashar Assad is an Alawite.
The party leader was quoted as saying there was "no doubt" national security was in serious jeopardy because the "state has demonstrated that it is unable to provide security for an entire sect under siege."
He said his supporters are working to ensure Shiites in the northern city are protected from their Sunni rivals.
Lebanon broke free of Syrian domination with its Cedar Revolution in 2005. Civil war raging in neighboring Syria has threatened to spill over Lebanon's borders.