Deadly clashes have erupted in the Lebanese capital Beirut and residents blocked roads in the country's northern region of Akkar near the city of Tripoli after soldiers there killed two members of an anti-Syrian opposition alliance.
Gunmen fired rocket-propelled grenades and machine guns early on Monday in intense street battles in Beirut, killing two people and wounding at least 18 others.
"There is an uneasy calm.. streets are relatively empty," Al Jazeera's Zeina Khodr reported from Beirut.
"The situation overnight, the clashes that were witnessed in Beirut, were the worst since January 2001 when we saw people take to the streets in protest following the collapse of the government of the former Prime Minister Saad al-Hariri.
"People who took to the streets were supporters of Saad al-Hariri's movement, mainly Sunnis. they were protesting the death and killing of a Sunni cleric and his bodyguard in northern Lebanon."
The clashes erupted hours after Sheikh Ahmed Abdul Wahid, a Sunni Muslim religious leader, and Muhammed Hussein Miraib, both members of the March 14 alliance, were shot in their car near Tripoli on Sunday as they "sped through a Lebanese army checkpoint without stopping".
The fighting, some of the worst in Beirut in years, exacerbated deep political and sectarian divisions, as fears mounted that the conflict in neighbouring Syria was spilling across the border.
Crisis in Syria
Our correspondent, reporting from Tripoli on Sunday, said that people in the area had already drawn their own conclusions about the incident and believed the army officer who carried out the shootings was allied with the Syrian government of President Bashar al-Assad.
"The bottom line is this: Syria yet again is a dividing issue in this country. The rival groups are divided in their support and opposition to the Syrian government. And this is where the fear lies," Khodr said on Monday.
"The very fact that the Lebanese army is at the centre of the conflict makes the situation more dangerous. Because the army has always been seen as the neutral institution, the only institution that can hold this politically unstable country together."
In-depth coverage of escalating violence across Syria
Over the past week Alawites, the sect to which Assad belongs, and Sunnis have been fighting each other in Tripoli, Khodr said.
"What has become clear here is that Lebanon can no longer continue with its policy of disassociating itself with the turmoil just across the border," Kodr said.
"The Sunni cleric's funeral will be held later today [Monday] and already there are tensions in the north. It's not clear if we will witness more violence, but what is clear is that as long as there is no solution to the Syrian crisis, this country will be in danger."
Najib Mikati, the Lebanese prime minister, tried to quell growing tensions on Sunday.
"The government is determined to continue to shoulder its national responsibilities amid this critical period in Lebanon and the region, and it will take all measures necessary to preserve civil peace," he said in a statement.
The clashes in Beirut occurred in the neighbourhood of Tarek Jadidah. Sources said they pitted two Sunni factions against each other; one that opposes Assad, and another loyal to a Sunni political figure, Shaker Berjawi, who supports the Syrian president.
Lebanon's army released a statement confirming the deaths at the checkpoint but did not give any information on who was responsible or what led to the shooting.
"The leadership of the army expresses deep regret for the death of the two victims ... It will immediately form an investigative committee comprised of senior officers and military police under the relevant court," the statement said.
Some troops had recently pulled out of Akkar to prevent tensions from escalating after sporadic fighting over the past week, a security source said.
Khaled Daher, a member of parliament from the Future Movement party, which is part of the March 14 alliance, said the two men were targeted.
"If shots were fired at the tyres, we would say there was a mistake. But we consider this a direct targeting from the army," he told Reuters news agency.
"Frankly, we do not want to see the army here because it works at the service of the Syrian regime," he said.
Many Sunni Muslims in Lebanon's north sympathise with Syria's uprising against Assad and say that the Lebanese army is taking orders from Damascus.
Syrian government troops were garrisoned in Lebanon until 2005.
Beirut-based political commentator Rami Khouri said the recent violence in Tripoli that killed at least eight people and wounded dozens had been linked to events in Syria.
"You have tensions in the area going back years but this has been exacerbated by the situation in Syria ... Syria is not the primary factor, but it is related," he said.