TRIPOLI, Lebanon (AFP) — The Lebanese army opened fire early Monday after a homemade bomb was thrown in an area of the northern city of Tripoli that has seen bloody clashes since May between two rival factions, an army spokesman told AFP.

"The army fired at the place from where the bomb was thrown, in a sector separating (Sunni-majority) Bab al-Tebbaneh and Jabal Mohsen" where Alawites live, the spokesman said.

Witnesses told AFP that two bombs had been thrown and an exchange of fire ensued between the two sides for 10 minutes before the army intervened.

The spokesman said no one had been hurt.

At least 23 people have been killed since the violence started in May between the residents of Jabal Mohsen, who mostly back the opposition led by the Shiite Hezbollah, and those of Bab al-Tebbaneh who support the anti-Syrian majority.

Troops have rarely intervened in the clashes, drawing criticism from the anti-Syrian group.

There has been tension between the two communities ever since Lebanon's 1975-1990 civil war. Alawites are an offshoot of Shiite Islam and straddle the border into Syria whose President Bashar al-Assad is a follower of the faith.

Monday's incident followed a decision by the supreme defence council to step up security measures over all of Lebanon after a bomb attack Wednesday that killed 14 people including nine soldiers in the centre of Tripoli.