At least nine people have been killed in clashes between Syrian government forces and activists in neighbouring Lebanon.
Over the past few weeks violence has escalated in the port of Tripoli, 43 miles north of Beirut, between Sunni Muslims and pro-President Bashar al-Assad members of the Alawite community.
The death toll on Saturday was the highest in a single day, raising fears that Syria's unrest could spill over into its neighbour.
Residents reported the dead victims included civilians caught in the crossfire and more than 40 people had been wounded.
The two sides reportedly exchanged fire with machine guns and rocket propelled grenades.
The Lebanese National News Agency said there was "shelling across both areas heard every five minutes, and snipers targeting civilians".
The army moved into the area with armoured vehicles but did not open fire, a Reuters journalist at the scene said.
The violence has prompted Lebanese Prime Minister Najib Mikati to travel to the northern city and hold talks with ministers and officials to try to stop the violence.
"The Lebanese army and internal security forces need to take all measures to stop the clashes in the city of Tripoli, without discrimination," a statement from Mr Mikati's office said.
Syria flooded Lebanon with troops early in its 1975-1991 civil war and dominated its neighbour for more than a decade afterwards.
It retains significant influence over Lebanon's intelligence apparatus and military, despite having withdrawn troops in 2005.
United Nations peace envoy Kofi Annan said on Saturday that Syria was slipping towards all-out civil war and that the entire region could suffer if the international community did not step up pressure on Mr Assad.
The UN says forces loyal to Mr Assad have killed more that 9,000 people during the revolt in Syria.