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JERUSALEM - Lebanon's second-biggest city saw its fourth consecutive day of violence today between groups supporting and opposing Syrian President Bashar al-Assad.

The sectarian fighting, some of the worst since Lebanon's bloody 15-year civil war, has left at least a dozen people dead and re-ignited fears that the 17-month uprising in neighboring Syria could have wider regional implications.

Local media described a tentative peace broken in the northern port city of Tripoli today, with reports of one man killed by a sniper. Sniper fire and explosions from rocket-propelled grenades were heard overnight and into the morning.

At least 12 people have been killed since Monday with more than 70 wounded, including 11 soldiers called in to quell the violence, according to the Daily Star newspaper.

The violence started Monday between two areas in Tripoli: a Sunni Muslim neighborhood that is anti-Assad, and another that supports Assad and that, like Assad, is Alawite, an offshoot of Shia Islam. The two areas are divided by an avenue called Syria Street.

The fighting follows tit-for-tat kidnappings that have seen Lebanese Shiites abducted in Syria and Syrian rebels kidnapped by a powerful clan in Lebanon. It is also the latest in a string of flare-ups between the Sunnis and Alawites in Tripoli since the Syrian uprising started last March.

Lebanese Prime Minister Najib Miqati warned Wednesday that the violence is "efforts to drag Lebanon more and more into the conflict in Syria when what is required is for leaders to cooperate … to protect Lebanon from the danger."

Activists inside Syria on Thursday reported renewed fighting in Syria's two biggest cities, Damascus and Aleppo. Government troops reportedly clashed with rebel forces, pushing up from the southern edge of the Damascus. They also shelled neighborhoods from the Qasioun mountain overlooking the north of the city.

In the past few weeks, much of the focus of the fighting has been on the commercial capital of Aleppo, Syria's biggest city. Rebel fighters have faced tanks, helicopter gunships and fighter jets, with claims of victory and control coming from both sides.

"Civilians are enduring a horrific level of violence in the battle between Syrian government forces and opposition fighters for control of Aleppo," Amnesty International said today in a new report following a 10-day stay in the city. "The use of imprecise weapons, such as unguided bombs, artillery shells and mortars by government forces has dramatically increased the danger for civilians," said the group's Donatella Rovera.

The Britain-based opposition group Syrian Observatory for Human Rights said more than 100 people were killed across the country today while some 250 were killed Wednesday.

"The situation has just got worse over there," Finnish Lieutenant Commander Mikko Suomela told newspaper Helsingin Sanomat upon arriving home after the four-month United Nations monitoring mission ended over the weekend. "The fighting has escalated from sporadic outbreaks to cover almost the entire country," he said. At some point, undoubtedly, there will be peace, but I'm afraid that it will take some time. It doesn't look good."