Sniper fire from both supporters and opponents of Syrian President Bashar Assad was heard throughout the night and early Tuesday morning in the neighborhoods of Jabal Mohsen and Bab al-Tabbaneh, The (Beirut) Daily Star reported.
Marwan Charbel, the caretaker interior minister, described the fighting as a "tragedy." He said it was a sign that fighters in Tripoli have ignored their superiors and are operating independently.
Speaking at a news conference, Charbel said the Lebanese army was working along the border with Syria "within its capabilities."
He said patrolling the full length of the border required 100,000 soldiers, plus the installation of a monitoring system, which he said was not feasible.
At least six people have been killed and more than 42 wounded in Tripoli since Sunday.