Lebanese tanks were out on the streets of Tripoli on Saturday after nine people including a boy were killed in sectarian fighting which raged through the night in the northern port city.
Militants from the rival Sunni Muslim and Alawite communities battled with rocket-propelled grenades and automatic weapons in the latest bout of violence to rock the Mediterranean city.
"The army is working for real calm in the north," an army official told AFP, but added: "Security requires political agreement."
Lebanon has been hit by sporadic outbreaks of violence despite a power-sharing deal between rival political factions in May which led to the election of Michel Sleiman as president and the creation of a unity cabinet.
The latest unrest comes after the new cabinet hit snags in deliberations aimed at drawing up a policy agenda ahead of a parliamentary vote of confidence which would enable the government to be officially installed.
The army was on high alert, with tanks and armoured vehicles patrolling the streets to keep the peace between fighters in the mainly Sunni Bab al-Tebbaneh district and the neighbouring largely Alawite area of Jabal Mohsen.
Among the dead were a 10-year-old boy and two women, while another 50 people were injured in the fighting that first erupted early Friday, the security official told AFP.
Intense fighting raged through the night despite a ceasefire that went into effect at 1500 GMT on Friday, but by Saturday morning the situation was generally calm.
However, residents of Bab al-Tebbaneh were blocking a motorway to the border with Syria with rocks and tyres in protest at the arrest of two fellow inhabitants over the fighting.
Shops in the area were closed and many families who evacuated their homes near the main battle zone were taking refuge in schools, an AFP correspondent said.
"The army has sent reinforcements to the battle zones to secure the ceasefire and the army command has promised us to firmly respond to any violation of the ceasefire," Sunni MP Mohammed Abdel Latif Kabbara of the parliamentary ruling majority said.
Interior Minister Ziad Barud and the head of the internal security forces Ashraf Rifi headed to Tripoli late Friday to see the situation for themselves and to assess measures to restore calm.
Bab al-Tebbaneh is a stronghold of the anti-Syrian parliamentary majority while the inhabitants of Jabal Mohsen are mainly supporters of the mainly Shiite opposition led by the powerful Hezbollah movement.
Tensions between the two communities date back to Lebanon's 1975-1990 civil war. Alawites are an offshoot of Shiite Islam who revere Imam Ali, the cousin and son-in-law of the Prophet Mohammed.
The Lebanese army deployed in force in the city in mid-July, pledging a tough response to any breach of security. Clashes between the two sides have killed 16 people and wounded more than 100 since June.
In Friday's violence, a rocket-propelled grenade slammed into an apartment building near a vegetable market, setting it ablaze, while another one hit a mosque in Bab al-Tebbaneh, an AFP correspondent said.
"Every time a sectarian rift breaks out in the north, it is used for political pressure... weapons are being used as a way of making political gains," said majority MP and former sports minister Ahmed Fatfat.
Friday's violence erupted after cabinet ministers decided on Thursday night to postpone talks on the issue of weapons held by Hezbollah, the powerful Shiite Muslim political opposition movement and militia.