Shelling between two pro- and anti-Syrian neighbourhoods in the north Lebanon port city of Tripoli on Friday left three people wounded, a security official and hospital sources said.
The security official said at least four shells and grenades fell on the two districts -- one with a majority Sunni Muslim population supporting the revolt in neighbouring Syria and another populated by Alawites loyal to the Syrian regime -- in early evening.
Clashes in the area over the past week have left 10 people dead and sparked fears that the revolt sweeping Syria since March of last year could engulf Lebanon.
Tension between the Sunni and Alawite communities in Tripoli has been fueled by the uprising in Syria and the arrival in the area of thousands of Syrian refugees fleeing the violence in their country.
Clashes broke out last weekend after the arrest of a Sunni Islamist on charges of belonging to a terrorist organisation.
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His supporters say he was targeted for helping Syrian refugees fleeing the unrest in their country.
Prime Minister Najib Mikati, who hails from Tripoli, warned at a cabinet meeting this week that the "fire was smouldering under the ashes" in the port city.
Since the outbreak of the uprising against Syrian President Bashar al-Assad in March 2011, Tripoli has become a safe haven for activists and thousands of refugees fleeing the unrest that has left more than 12,000 people dead, according to a rights group.
Sectarian violence has flared on a number of occasions in the city since the revolt broke out but the latest escalation has been the deadliest.
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.
The Alawite sect is an offshoot of Shiite Islam to which Assad belongs and which has controlled Syrian politics for decades.