BEIRUT — Lebanese troops launched a major security operation on Monday to open all roads and force gunmen off the streets, trying to contain an outburst of violence set off by the assassination of a top intelligence official who was a powerful opponent of Syria.
Sectarian clashes killed at least five people.
Opponents of Syria have blamed the regime in Damascus for the killing of Lebanese Brig. Gen. Wissam al-Hassan in a Beirut car bomb on Friday.
With Lebanon already tense and deeply divided over the civil war next door, the assassination has threatened to drag the country back into the kind of sectarian strife that plagued it for decades -- much of it linked to Syria.
"The nation is passing through a crucial and critical period and tension has risen in some areas to unprecedented levels," the army said in a statement. It urged politicians to be careful not to incite violence "because the fate of the nation is on the edge."
"Security is a red line," the statement said, adding that strict measures are being taken to "prevent Lebanon from being an arena for settling regional problems."
Cracks of gunfire rang out in Beirut as soldiers and armored personnel carriers with heavy machine guns took up position on major thoroughfares and dismantled roadblocks.
The state news agency reported sporadic gunfire in parts of Beirut and around the northern city of Tripoli.
Tripoli saw clashes between two neighborhoods that support opposite sides in Syria's conflict and have a decades-long history of shooting at each other.
Four people were killed in the fighting between the Sunni neighborhood of Bab Tabbaneh and the adjacent Alawite neighborhood of Jabal Mohsen, which supports the Syrian regime.
Lebanon and Syria share similar sectarian divides that have fed tensions in both countries. Most of Lebanon's Sunnis have backed Syria's mainly Sunni rebels, while Lebanese Shiites tend to back President Bashar Assad who belongs to the minority Alawite sect — an offshoot of Shiite Islam.
Tripoli residents said scores of soldiers deployed around the city in an attempt to bring back calm. The military also set up checkpoints, searched cars and asked people for identity cards.
Security officials also said one man was killed in the Wadi Zayneh area north of the southern city of Sidon. They said the clashes also wounded at least six people in Beirut and 11 in Tripoli.
The officials spoke on the condition of anonymity because they were not authorized to speak to the media.
Gen. al-Hassan, the assassinated intelligence official, was a Sunni who challenged Syria and its powerful Lebanese ally, the Shiite militant group Hezbollah. His killing has imperiled Lebanon's fragile political balance.
Many politicians blamed Syria for the killing and angry protesters tried to storm the government palace after Gen. al-Hassan's funeral on Sunday, venting their rage at leaders they consider puppets of a murderous Syrian regime.
But they were pushed back by troops who fired their guns in the air and filled the street with tear gas.
Prime Minister Najib Mikati, a Sunni, told As-Safir newspaper that when he took up his post last year, he intended to protect all Lebanese, particularly Sunnis.
"I was convinced that through this mission, I am protecting my country, my people and especially fellow members of my sect," he said.
The prime minister of Lebanon is usually a Sunni according to a sectarian division of top posts in the state. Over the past year, pro-Syrian Hezbollah and its allies have come to dominate the government.
On Sunday night, a group of anti-Syrian protesters started an open-ended sit-in outside Mr. Mikati's house in his hometown of Tripoli. The protesters said they will only end the sit-in when Mr. Mikati resigns.