Lebanon's army began deploying Monday in the northern city of Tripoli following a week of bloodshed in which 14 people died and more than 80 were wounded, an AFP reporter said.
The fighting, between supporters and opponents of Syria's regime, has been concentrated in the Bab al-Tebbaneh and Jabal Mohsen districts of Tripoli, Lebanon's second city.
The reporter said tanks and jeeps entered the northern sector of Bab al-Tebbaneh but their progress was slowed by sniper fire, to which the troops responded. One soldier was wounded in the firing.
A security official said the army had also deployed in Jabal Mohsen, which adjoins Bab al-Tebbaneh.
Residents of Bab al-Tebbaneh support the revolt against Syrian President Bashar al-Assad, while those in Jabal Mohsen back Assad. They have fought frequently since the Syrian conflict erupted in March 2011.
Acting Prime Minister Najib Mikati said on Saturday that "security forces will take every step to put an end to the violence and chaos" in the city. "They will be strict and impartial."
But residents of Syria Street, which separates the two rival neighbourhoods, were sceptical.
"This is all a joke. It is the eighteenth time since May, 2008 that they come to help. In fact, the army makes a small tour and then leaves. There is no solution," said Mustapha al-Hajj, a 69-year-old retired man.
"In the past eight days, 400 families have left Syria Street, including my own. We sleep under the stars, me, my wife and our three children, in a park in the city," he said.
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"Each month it's the same thing," he added despairingly.
Since the start of the latest violence, six residents of Jabal Mohsen, where the majority adhere to the same Alawite branch of Shiite Islam as Assad, have been killed, while eight residents of the mainly-Sunni Bab el-Tebbaneh suburb have died.
Tripoli is home to 200,000 people, 80 percent of whom are Sunni Muslims, 6-7 percent Alawites and the rest Christians.
The fighting broke out on October 21 as a Lebanese private television aired an interview with Assad, in which he said the time is not ripe for a peace conference to try to resolve the 31-month conflict and said he was ready to run for re-election in 2014.
The violence prompted residents to flee the impoverished neighbourhoods, and schools and universities have been closed since the middle of last week.
Lebanon is deeply divided into pro- and anti-Damascus camps.
The division has widened since Lebanese Shiite movement Hezbollah admitted in May it was sending fighters into Syria to support Assad's troops.
Small radical Sunni organisations have also sent men across the border to fight alongside rebels.
Lebanon was dominated politically and militarily by Damascus for 30 years until 2005.