A blast targeting a military bus on the outskirts of the northern Lebanese port city of Tripoli resulted in at least 6 dead on Monday, Lebanese security sources said.

"We have at least six people killed, three of them soldiers," the sources said.

Hospital officials in Tripoli said at least 30 people who sustained medium and serious injuries had been admitted.

A police officer at the scene told Deutsche Presse-Agentur dpa that the bomb went off at the southern entrance of the city as the mini-bus was heading towards the capital Beirut during morning rush- hour.

A witness said 24 passengers were on board.

Police and the army immediately cordoned off the area as forensic experts began gathering evidence.

People at the scene were seen wailing and crying, trying to get information about loved ones who were on the bus.

The force of the blast shattered windows and damaged cars nearby.

According to initial investigation the bomb was placed in a car and was detonated by remote control as the bus drove by.

There was no immediate claim of responsibility.

A similar explosion in August left 14 people dead, nine of them soldiers, in the deadliest attack in the troubled country in three years.

Tripoli has been rocked by deadly sectarian violence in recent months.

In June and July, 23 people were killed in battles between Sunni Muslim supporters of Lebanon's anti-Syrian ruling majority and and their Damascus-backed rivals from the Alawite community.

Monday's explosion came as Lebanon's rival factions have been working toward resolving their differences following an 18-month political crisis that brought the country to the brink of civil war in May.

The Tripoli blast also came two days after a bombing left 17 people dead in the capital of neighbouring Syria, Lebanon's former powerbroker.