Weekend clashes across Lebanon following the assassination of a security chief spilled into Monday, prompting troops to unleash security operations, and leading to mounting concerns that the uprising in Syria is crossing into the bordering state.
The clashes began when Gen Wissam al-Hassan, a Sunni Muslim and the head of the intelligence branch of the Internal Security Forces, was killed in a car bomb on Friday. BBC news reports that
Opposition figures blamed the attack on the Syrian government.
Lebanon's religious communities are divided between those who support the Syrian government - including many Shias - and those mostly from the Sunni community who back the rebels.
Gen Hassan was an outspoken critic of Syrian President Bashar al-Assad, who is a member of the Alawite sect, an offshoot of Shia Islam.
Mr Hassan also had close links to the opposition 14 March alliance and the family of its leader, former Prime Minister Saad Hariri.
Prime Minister Najib Mikati - a Sunni - offered to resign, but this was rejected by the president.
Intense clashes were seen in Tripoli and Beirut, which left at least 50 wounded and several, including a child, dead.
The army put heavily armed troops on the streets to quell the unrest.
The army command said in its statement that Lebanon was going through a critical time.
"We will take decisive measures, especially in areas with rising religious and sectarian tensions, to prevent Lebanon being transformed again into a place for regional settling of scores, and to prevent the assassination of the martyr Wissam al-Hassan being used to assassinate a whole country," it said.
Troops in full combat gear and armoured personnel carriers stood guard at traffic intersections and government offices, with barbed wire and concrete blocks protecting buildings.
Al Jazeera adds that "several people were wounded after the army made a pre-dawn sweep through the district of Tariq Jdideh [in Beirut on Monday] in pursuit of armed men, and automatic weapons and anti-tank rocket fire could be heard."
* * *
Al Jazeera video: Funeral for slain Lebanon official ends in violence
Video from Agence France-Presse shows troops firing tear gas at protesters.