Sporadic gun and rocket fire broke out at midnight and continued through the night, forcing some residents of the port city to flee their homes, the official told AFP on condition of anonymity.

In May, street battles raged in Tripoli between the neighbourhoods of Jabal Mohsen, mainly populated by pro-Damascus Alawites, and Bab al-Tebbaneh, home to Sunnis who support the opposition seeking to oust President Bashar al-Assad.

Sectarian violence has flared on a number of occasions in the city since the revolt broke out in neighbouring Syria in March last year.

It reflects a deep split between Lebanon's political parties where the opposition backs those leading the revolt in Syria while a ruling coalition led by the powerful Shiite Hezbollah supports Assad's regime.