Sectarian violence linked to the unrest in neighbouring Syria shook the northern Lebanese city of Tripoli on Sunday, with the state news agency reporting a soldier and two civilians killed in the street clashes.

The fighting highlights how easily trouble in Syria can raise tensions in Lebanon, with which it shares a complex web of political and sectarian ties and rivalries.

Residents say gunfire broke out in the city Saturday and continued through the night primarily between a neighbourhood populated by Sunni Muslims who hate Syrian President Bashar al-Assad and another area with many Assad backers from his Alawite sect.

Lebanon's national news agency NNA said one soldier was shot dead by a sniper in the city early Sunday. Another man was found dead on the side of a road while a third died after a shell landed in a residential neighbourhood.

An Associated Press reporter in the city said the Lebanese army sent reinforcements to the city, but that gunmen still patrolled the streets and intermittently shot at each other with automatic rifles. Heavier weapons, like rocket-propelled grenades, have also been fired.

Similar clashes in the area in February killed two people.

The fourteen month-old conflict in Syria has exacerbated sectarian and political tensions in Lebanon, and many fear Syria's chaos will eventually bleed across the border.

Lebanon is sharply split along sectarian lines, with 18 religious sects. But it also has a fragile political fault line precisely over the issue of Syria.

An array of pro-Syrian parties support Assad's regime, as do many Lebanese citizens. Others hate Assad and accuse Damascus of heavy-handed meddling in Lebanese politics.

The two sides are the legacy of, and backlash against, Syria's virtual rule over Lebanon from 1976 to 2005 and its continued influence since.