TRIPOLI - Five people were killed in fierce sectarian clashes in Lebanon's northern port of Tripoli on Friday as fighters exchanged rocket-propelled grenades and sniper fire, a security official said.

Two women were among the victims, the official told AFP on condition of anonymity, adding that another 22 people were wounded before a ceasefire took hold.

"The ceasefire went into effect at exactly 6:00 pm (1500 GMT)," the official said.

He said most of those hurt were caught in crossfire between fighters in the mainly Sunni Bab al-Tebbaneh district and the neighbouring largely Alawite area of Jabal Mohsen, while at least one person was wounded by a sniper.

A rocket-propelled grenade (RPG) 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.

Bab al-Tebbaneh is a stronghold of the anti-Syrian parliamentary majority while the inhabitants of Jabal Mohsen are mainly supporters of the Shiite Hezbollah-led opposition.

Fighting broke out overnight and raged during the morning, the correspondent said, adding that the sound of exploding RPGs were also heard intermittently in the afternoon.

A first ceasefire announced for 12:30 pm (0930 GMT) by the Sunni mufti of northern Lebanon, Malek al-Shaar, after a meeting of political and religious officials in Tripoli, failed to take hold.

Sunni MP Mohammed Abdel Latif Kabbara of the parliamentary ruling majority said a new ceasefire would go into effect at 6:00 pm and that the army would take action against anyone violating the truce.

"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," Kabbara said.

Shopkeepers in the area kept their stores shut on Friday because of the violence and people were seen fleeing their homes near the front lines, the AFP correspondent said.

Families who stayed behind took cover inside shops and underground garages as hundreds of gunmen took to the streets in full sight of the army which stood by without intervening, the correspondent added.

Earlier an army spokesman told AFP that soldiers "cannot intervene and use force because the neighbourhoods are densely populated."

"The shooting is from inside buildings and we cannot use our artillery because civilians could get killed or wounded."

Loudspeakers urged people to stay where they were and not make their way to mosques for Friday prayers, as is customary, because of the fighting.

"Our home is in a dangerous area," said Ali al-Shaykh, a father of seven.

"We left our home at three in the morning and now we're sheltering in a mosque with about 70 other families," he added.

The Lebanese army deployed in force in the city in mid-July, pledging a tough response to any breach of security.

Repeated clashes between the two sides have killed 14 people and wounded more than 100 since June.

Alawites are an offshoot of Shiite Islam who revere Imam Ali, the cousin and son-in-law of the Prophet Mohammed.

Majority MP and former sports minister Ahmed Fatfat said in a statement that "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."

The latest fighting comes after the newly formed 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 cabinet decided on Thursday night to postpone talks on the issue of Hezbollah's arms.