Lebanese troops have deployed in the northern city of Tripoli to end fierce fighting between Hezbollah sympathisers and supporters of the government.
Thousands fled their homes as several people were reportedly killed in heavy exchanges of machine gun fire and rocket-propelled grenades.
Meanwhile, an uneasy calm has descended on Beirut, after four days of running street battles left 38 people dead.
The clashes have triggered fears of a return to Lebanon's 15-year civil war.
On Saturday, Hezbollah agreed to pull its fighters off the streets of the Muslim western Beirut after the army overturned government measures aimed at curbing the group.
But many roads remain blocked, including the airport road, as the Iranian-backed Shia group continues its campaign of civil disobedience.
Arab foreign ministers are currently holding an emergency meeting on the crisis in the Egyptian capital Cairo.
In Tripoli, Sunni supporters of the Western-backed government have reportedly been fighting members of an Alawite sect loyal to Hezbollah.
About 7,000 people have fled from the city's Bab al-Tebbaneh district, which marks the front line, reports said.
Earlier, pro-government demonstrators burned the offices of the pro-Syrian Baath Party.
They stamped on posters of Syrian President Bashar Assad and Hezbollah leader Hassan Nasrallah.
They could also be seen throwing furniture and files from the Baath offices and a local opposition politician's office.
The confrontation in Beirut eased off after the army offered a face-saving compromise that allowed the government to back down from two controversial decisions.
The government had moved to shut down Hezbollah's telecoms network and remove the chief of security at Beirut airport for alleged sympathies with the guerrillas.
The army has essentially shelved both measures after they triggered a devastating Hezbollah onslaught, the BBC's Jim Muir reports from Beirut.
Managing to retain its unity and the respect of both sides, the army has emerged as the arbiter in the current crisis, our correspondent says.
If all goes well, the army initiative should restore calm on the streets and see the international airport reopen.
While it does not address the fundamental political deadlock underlying the eruption of violence, it has created a problem-solving mechanism that may help movement in that direction.
Our correspondent notes that all parties agree that the army commander, Gen Michel Suleiman, should be Lebanon's next president.
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