BEIRUT - Opponents and supporters of Syrian President Bashar al-Assad traded heavy machine-gun fire and mortar shells in the Lebanese port city of Tripoli, leaving five people dead in what was described as some of the heaviest fighting there in years, officials said Thursday.

Tripoli has been a frequent flashpoint of sectarian tensions stoked by the civil war in neighboring Syria. The latest overnight deaths brought to 16 the number of people killed in clashes there this week, and the overall number of wounded rose to 190, said a security official who spoke on condition of anonymity in line with military regulations.

In comments by Lebanon's state-run National News Agency, cabinet minister Faisal Karami said the fighting was among the worst in the city since Lebanon's 15-year civil war, which ended in 1990.

Regime supporters and opponents live close to each other in the city. The divisions largely run along ethnic lines, with many Sunni Muslims supporting the Syrian rebels and Alawites, or followers of an offshoot of Shiite Islam, backing the regime. Assad is an Alawite.

The spike in Tripoli tensions has been linked to a Syrian regime offensive against the rebel-held city of Qusair in western Syria this week. The battle has pitted regime forces and fighters from Lebanon's Hezbollah militia, a regime ally, against rebel units.

Fighting in Qusair continued for a fifth day Thursday, after Syrian opposition leaders urged rebels from elsewhere to converge on the town, which is strategically important to both sides.

The regime would solidify control in the heavily populated west if it retakes the town which links the capital Damascus with the Alawite heartland along the Mediterranean cost.

For the rebels, predominantly Sunni Qusair is part of a supply line of weapons and fighters from nearby Lebanon.

The Britain-based Syrian Observatory for Human Rights, a pro-opposition group, said Thursday that 46 Hezbollah fighters have been killed in the battle for Qusair.

In the past, Hezbollah tried to play down its involvement in the civil war, but its high-profile role in Qusair has made that impossible. Hezbollah has held funerals for fighters who officials close to the group say died at Qusair.