Lebanese army soldiers step down stairs carefully during clashes Tuesday in the old market of the northern port city of Tripoli, Lebanon. (Hussein Malla/AP)

A small but increasingly vocal number of Lebanon’s Sunni Muslims are backing Islamist leaders’ calls for regime change in neighboring Syria and voicing their fierce discontent with their own government, a sign that the sectarianism splitting Syria may be deepening Lebanon’s longstanding divides.

Rallying in the central square of this northern city, hundreds of men, many of them followers of the Salafi branch of Sunni Islam, have spent more than two weeks protesting the detention without charge of dozens of Sunnis in Lebanon and calling for the downfall of President Bashar al-Assad in Syria.

Inspired, they say, by the largely Sunni uprising in Syria, the group has refused to leave the square, even after clashes with security forces last week ignited days of fighting between Sunnis and minority Alawites in Tripoli. Sectarian tension has worsened during 14 months of Syrian unrest as Syrian refugees and wounded fighters have flooded into the city.

“What happened in Syria — and in Tunisia, Egypt, Yemen — let us smell the beautiful smell of freedom,” Omar Bakri Mohammed, a prominent Salafi leader, said Tuesday, surrounded by supporters in al-Nour Square. Criticizing the Lebanese government for closeness to Assad, he said that the sit-in would encourage authorities to “take us seriously for once in their lives,” darkly hinting that the protesters may in the future want to remove the Lebanese government entirely.

Violence in Syria showed no signs of ebbing Tuesday, as a bomb attack struck a convoy of vehicles in Idlib province that were part of a U.N. monitoring mission. No U.N. observers were hurt, but as many as 21 people were killed in the attack, according to activists.

Analysts attribute the surge in assertiveness among Tripoli’s Sunnis to a series of political shifts and security incidents that have left Lebanon’s Sunni society and political groupings marginalized. The Shiite political party and militia Hezbollah, meanwhile, has steadily increased its dominance over the country, which still bears the scars of a sectarian civil war that ended 20 years ago.

From the assassination of Sunni former premier Rafiq al-Hariri in 2005, to a display of force by Hezbollah when it took over part of Beirut in May 2008, to the 2011 fall of the government led by Hariri’s son, Saad, under pressure from a Hezbollah-dominated political bloc, many Sunnis have been left feeling deeply disenfranchised.

“It’s been defeat after defeat,” said Paul Salem of the Carnegie Middle East Center in Beirut. The presence both of unarmed Sunni protesters and armed Sunni fighters on the streets of Tripoli, Salem added, may have been prompted by a confluence of issues including a sense of empowerment after the uprisings in the Arab world as well as anger at the brutal treatment of Sunnis in Syria.

“This is a ratcheting up by the Sunnis of the north as to the level at which they can express a view on the Syrian issue, display their guns openly and defy some of the parts of the government which are Hezbollah-dominated,” Salem said.

In Tripoli, politicians and protesters struck a defiant tone. “We are expressing our right to support the Syrian revolution in facing a regime which is killing its unarmed people with tanks and air force,” said Hassan Khayal, of the political bureau of al-Jamaa al-Islamiya, the Lebanese branch of the moderate Sunni Muslim Brotherhood group.

The spark that triggered violence in al-Nour Square after 10 days of a peaceful sit-in came when a local man with ties to Salafi groups was arrested Saturday in connection with links to terrorist groups.

A spokesman for the Lebanese security forces confirmed that Shadi al-Mawlawi was informed that he should come to a center in Tripoli that distributes money to the needy to collect a contribution for hospital treatment for a relative. Once there, he was detained under suspicion of communicating with an al-Qaeda member, but not immediately charged. The arrest sparked outrage among the demonstrators who had been calling for the release of Sunnis detained without charge, and as the peaceful sit-in became an angry mob, shots were fired at security forces.

Accounts of what happened next vary, but Khayal and local residents report that a teenage Sunni boy was shot and killed in the flashpoint Sunni Bab al-Tabbaneh neighborhood. The impoverished cluster of high-rises sits alongside the Jabal Mohsen area, home to a community mostly composed of Alawites, the Shiite offshoot faith that Syria’s Assad also follows.

Fighting between the Sunnis, who support the Syrian uprising, and Alawites, who side with president Assad, did not die down until Monday night. Eight civilians were killed, as were two members of the security forces, said the security forces spokesman.

In Jabal Mohsen on Tuesday, one house with posters of Assad pasted up outside was a still-smoldering ruin inside. Fresh bullet holes dotted shabby apartments already plentifully sprayed with gunfire over the decades the neighborhood has served a barometer for the city’s Sunni-Alawite tensions. Hundreds of soldiers patrolled calm but tense streets.

Mustafa Alloush, the local coordinator of the Future movement, a large, moderate political group headed by Hariri and backed by most Sunnis in the country, said that the sit-in and the response to the arrest of Mawlawi represented an increase in numbers and influence by Islamist political leaders.

Alloush insisted that the number of people embracing Salafism remained small, but said that some young Sunnis, feeling failed by the Hariri-led Future group, may have become more influenced by Islamist figures with a more aggressively sectarian attitude.

“Tripoli definitely in general has major animosity with the Syrian regime,” Alloush said, “and what we are seeing now is essentially related to what’s happening in Syria.”