The fighting in Tripoli is concentrated between two impoverished, rival neighborhoods. The Bab Tabbaneh district is largely Sunni Muslim, as are most of the Syrian rebels fighting Assad's rule. Residents of Jabal Mohsen, a neighborhood perched on a hill, are mostly from his Alawite sect, an offshoot of Shiite Islam.
But the violence in recent days has taken a more ominous turn, spreading to include other parts of Tripoli as snipers took up positions on rooftops, and gunbattles and rocket fire raged out of control.
On Monday, schools, universities and some businesses were mostly closed as occasional gunfire rang out.
Tripoli's landmark Abu Ali Square usually packed with cars, pedestrians and shoppers was largely deserted as ambulances took casualties to hospitals.
Lebanese military armored vehicles patrolled, sometimes helping carry terrified civilians to safe places.
At one point, a brown BMW sped toward an army checkpoint near the square and screeched to a halt. The shaken driver jumped out and shouted to the troops, "I have two soldiers who were shot in the neck."
The officers ran toward him, looked at the wounded soldiers in the car and said, "Take them straight to the hospital." The car sped away.
A soldier said the two wounded officers had been off duty and were going home in the northern region of Akkar when they were hit by sniper fire.
On Sunday night, announcements were made through mosque loudspeakers for people to move to lower floors to avoid being hit by bullets or shells.
"I am worried about Tripoli," said Khaled Tutunji, who works at a construction material shop near Abu Ali Square. "In the past, we did not know who is a Sunni and who is Alawite," he said as he stood beside an armored personnel carrier as cracks of gunfire echoed from a distance.
Tensions soared in the city in August, following twin bombings outside Sunni mosques that killed 47 people and wounded scores.
Authorities arrested several members of the pro-Assad Arab Democratic Party on suspicion they were involved and they summoned the group's leader, Ali Eid, for questioning. He has refused to go to the police intelligence office, saying he did not trust them to be impartial.
His son, Rifaat, said his father is ready to go to any security agency other than the police intelligence office, which many pro-Syrians accuse of being dominated by anti-Assad officers.
Since he refused to show up for questioning, a wave of attacks against Alawites intensified and more than a dozen members of the sect have been shot in the legs in Sunni neighborhoods. An unknown group named "Families of the (mosque) Victims" claimed responsibility for the shootings.
Saturday's clashes erupted after an Alawite was shot in the leg while in a Sunni neighborhood.
Following the security meeting that included President Michel Suleiman and army commander Gen. Jean Kahwaji, Mikati said the army was to take charge of security for six months.
The army would carry out patrols and implement arrest warrants issued for fugitives in the city, he added.
In Beirut, a security official speaking on condition of anonymity because he was not authorized to talk to the media said 600 policemen from different parts of Lebanon will be sent to Tripoli to help improve security, working under the army's command.
Mazen Kotb, a curtain maker in Tripoli, said his business has fallen by 70 percent because of the tensions. Many of his clients were Alawites who don't dare to come to his shop, he said.
"What is happening in Tripoli pains my heart," Kotb said as he checked his Facebook page on a computer screen on his desk. He said he wanted to ask for a new identity card that does not include his sect, adding he fears he might be shot in the leg if he goes into Alawite areas.
The nearly 3-year-old civil war in Syria has killed more than 100,000 people.
Syrian state media said Monday that government troops captured the western town of Nabek near the frontier with Lebanon after five days of fighting. The Syrian military has been on the offensive in the western Qalamoun region that borders Lebanon to try to stop the flow of fighters and weapons.
Also in the Qalamoun region, fighting continued for control of an ancient, pro-government Christian village about 60 kilometers (40 miles) northeast of Damascus.
The government said six nuns were trapped in the village of Maaloula, after al-Qaida-linked rebels seized large parts of the area. Syrian army tanks were positioned around it as the fighting sent smoke wafting over the scenic village, nestled in hillsides.
Forces loyal to Assad are trying to keep rebels led by the al-Qaida-linked Jabhat al-Nusra, or Nusra Front, from advancing. Opposition fighters have taken control of several parts of the village since blowing up a checkpoint at its entrance Friday, according to reports by the state news agency and opposition activists.
Five nuns and Mother Superior Pelagia Sayaf were trapped in the Mar Takla Convent, which sits above Maaloula, according to SANA.
Syria's Social Affairs Minister Kindah al-Shammat demanded that countries supporting the rebels pressure them to release the nuns. Rebels have seized parts of Maaloula before, only to be driven out within a few days by government forces.
Also Monday, the U.N.'s top human rights official said a growing body of evidence collected by U.N. investigators points to the involvement of senior Syrian officials, including Assad, in crimes against humanity and war crimes.
Navi Pillay, who heads the U.N. Office of the High Commissioner for Human Rights, said "the scale and viciousness of the abuses being perpetrated by elements on both sides almost defies belief." She said the abuses including suspected massacres, chemical attacks, torture and rape are being well-documented by an expert U.N. panel of investigators.
"They've produced massive evidence," she told a news conference. "They point to the fact that the evidence indicates responsibility at the highest level of government, including the head of state."
Syrian Deputy Foreign Minister Faisal Mekdad was dismissive of Pillay's remarks.
"She has been talking nonsense for a long time and we don't listen to her," he told The Associated Press in The Hague.
Pillay said the lists of suspected criminals will remain sealed until requested by international or national authorities for a "credible investigation," and then possibly used for prosecution. The lists must be kept sealed "to preserve the presumption of innocence" until proper judicial probes can be done that could lead to trial, she said.
Pillay and the four-member U.N. panel on Syria war crimes chaired by Brazilian diplomat and scholar Paulo Sergio Pinheiro has previously said Assad's government and supporters and the rebels who oppose them have committed heinous war crimes in the civil war.
But this time, Pillay specifically referred to the president though she was careful to say she hadn't singled him out as a possible suspect on the secret lists.
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Associated Press writers Albert Aji in Damascus, Syria, Diaa Hadid in Beirut, John Heilprin in Geneva and Mike Corder in The Hague, Netherlands, contributed to this report.
