At least one person has been killed in the Lebanese city of Tripoli in clashes between supporters and opponents of Syria's President Bashar al-Assad, security officials say.
At least 12 people were injured, as the two sides fired guns and rocket-propelled grenades at each other.
The violence erupted after Friday prayers and continued overnight.
Tensions in the northern port city have mounted since the beginning of the uprising in Syria last March.
Residents said the RPGs were fired from the Sunni Muslim district of Bab al-Tabbana towards the Alawite district of Jabal Muhsin on Friday.
Footage by Reuters TV also showed gunmen taking cover on street corners and firing volleys of automatic gunfire.
Lebanese troops were later deployed in both districts, the army said in a statement.
It added that several soldiers were among the injured.
Tripoli is dominated by Sunni Muslims, who support the anti-Assad uprising in Syria.
Mr Assad is an Alawite, and members of the minority sect - an offshoot of Shia Islam - occupy key positions in the Syrian government and security forces.
Syria's majority Sunni community has been at the forefront of the revolt against the president and borne the brunt of the state's crackdown, which human rights groups say has left more than 7,000 people dead.