Lebanon has deployed troops to the northern city of Tripoli after at least 12 people were killed in fierce clashes between supporters and opponents of Syrian President Bashar al-Assad, local medics and security sources said.
Residents said relative peace had returned to the city since the soldiers deployed at around 7am local time (04:00 GMT) on Sunday, after gunmen exchanged heavy fire and rocket propelled grenades.
Al Jazeera's Zeina Khodr, reporting from Tripoli, said an "uneasy calm" had set in after the fighting.
"The Lebanese army has been deployed, but if you talk to anyone, they will say this is just a temporary truce," Khodr said on Sunday.
"The clashes really have become more and more frequent over the last few months. This conflict really is far from over," our correspondent added.
The latest clashes began after midnight on Friday and continued throughout Saturday until the army deployment.
Residents of the neighbouring districts have clashed repeatedly in recent weeks, but Saturday's death toll is the highest in a single day in Tripoli, raising fears that Syria's unrest was spilling over into its smaller neighbour.
Among the dead were a woman and her son, killed by a rocket in the Bab al-Tabanneh district, a mostly Sunni Muslim community which supports Syria's opposition, a security official said.
At least five were wounded in Jabal Mohsen, an area mainly populated by Alawites who support Syrian President Bashar al-Assad.
"Over recent months, people have been warning that the crisis in Syria was going to spill over into the country," Khodr said.
"It actually has spilled over, and it's becoming a dangerous reality."
Najib Mikati, the Lebanese prime minister, and other Tripoli politicians instructed security forces on Saturday to use an "iron fist" to quell the worst violence to shake Tripoli since the start of an uprising against Assad in neighbouring Syria.
The interior ministry said a plan was being drawn up to deploy army and internal security forces in the flashpoint neighbourhoods.
Several people were killed in similar clashes in May. The frontline of the deadly street battles was Syria Street, which divides the rival neighbourhoods.
Supporters of Assad allege that Bab al-Tabbaneh is an operational base of the Free Syrian Army, the armed opposition group seeking to overthrow the government.
The Lebanese opposition backs the revolt in Syria while a ruling coalition led by Hezbollah supports the Damascus leadership.