A sniper has killed a Sunni sheikh in the Lebanese city of Tripoli, sparking new clashes between pro- and anti-Syrian factions that dashed a tenuous truce, a security official has told the AFP news agency.

The death of 28-year-old Sheikh Khaled al-Baradei on Friday brought to 17 the number of people killed in fighting in the city over the past five days and stoked fears of a spillover of major violence from the conflict in neighbouring Syria.

A further 86 people have been wounded.

The exchanges of rocket-propelled grenade and small arms fire pitted anti-Syrian fighters from the Sunni Muslim Qobbeh district against those in support of Damascus from the neighbouring Alawite district of Jabal Mohsen.

The intensity of the exchanges sparked large fires in the two neighbourhoods in the east of the Mediterranean port city, Lebanon's second largest.

Al Jazeera's James Bays reporting from Tripoli on Friday said: "The authorities have been trying to contain this trouble for five days, but the killing of the sheikh could change this."

Bays added that the situation is "getting worse" as the conflict spreads to other areas of the city with reports of shops being burned down.

"Every time someone is killed – and the death toll here continues to rise – then that is just increasing the problems, there are more calls for revenge."

Families hammered holes through the walls of their apartments to escape to safety down makeshift ladders as the clashes raged.

Hundreds of soldiers with tanks and military vehicles have deployed on the aptly named Syria Street which acts both as the dividing line between the two districts and as the frontline when fighting erupts.

Public anger

Several families displaced by the fighting had returned to the two districts on Thursday to inspect the damage to their homes, as a truce agreed on Wednesday had appeared to take hold.

"I can no longer cope with this situation. In my house I have got three families who have fled the violence," said Ahmed Breiss, who runs a car workshop in Qobbeh.

"We have nothing to do with what's going on in Syria. We want to live in peace," he said.

The authorities have instructed the army and security forces "to bring the situation under control, to prohibit any armed presence and to arrest those implicated" in the violence, he said in a statement.

Al Jazeera's Bays said the army has tried to calm things down, "but they face a problem because they want to be a neutral player.

"They cant get go in too tough otherwise they’re going to end up being one of the participants."

A wave of kidnappings preceded the latest round of fighting and rattled the already fragile security situation in Lebanon, which lived under three decades of Syrian domination.

The United Nations has called for more international support for Lebanese authorities to prevent a spillover of the 17-month conflict in neighbouring Syria.

"The situation in Lebanon has become more precarious and the need for continued international support to the government and the Lebanese armed forces increasingly important," Jeffrey Feltman, the UN under secretary-general, said on Wednesday.

The latest unrest in Tripoli, which has been the scene of several deadly incidents over the past year, follows a wave of tit-for-tat kidnappings of Lebanese citizens in Syria and of Syrians living in Lebanon.