Nine people have been killed in 48 hours of clashes in Lebanon's northern town of Tripoli linked to the conflict in neighbouring Syria, a security source told AFP on Saturday.

The violence between two districts of the city caused local schools to close and cut traffic flow in the city to a trickle, an AFP correspondent said.

The clashes, which have also injured 50 people, pit the Alawite district of Jabal Mohsen against the neighbouring Sunni quarter of Bab al-Tebbaneh.

The latest fighting broke out on Thursday after a Sunni man was killed by unknown gunmen on a motorbike in central Tripoli.

But tensions between the districts have run high for decades, only increasing with the outbreak of the conflict in Syria, where Alawite President Bashar al-Assad faces a Sunni-dominated uprising.

On Saturday, two people were killed by snipers and another three succumbed to injuries sustained earlier in the clashes, the source said, raising the toll since Thursday to nine.

The Lebanese army has deployed in the city, arresting several people overnight and responding to sources of fire.

The war in Syria has deepened existing sectarian and political tensions in Lebanon, particularly between supporters of the Shiite movement Hezbollah, an Assad ally, and Sunni backers of former prime minister Saad Hariri who support the uprising.