Clashes between militants and the Lebanese army saw at least eight people in the city of Sidon on Sunday.
Six Lebanese soldiers and two gunmen linked to a militant Sunni cleric Ahmed al-Assir were killed after heavy fighting in southern Lebanon.
Nineteen soldiers and thirteen militants were wounded in the fighting.
The fighting even knocked out power throughout the country after gun and rocket fire likely damaged Zahrani-Aramoun power network.
The violence is linked to the Shia militant group Hezbollah's role in the Syrian uprising. Rebels in Syria consist mainly of Sunni fighters who oppose President Bashar al-Assad, an Alawite.
Hezbollah's presence in Syria has stirred sectarian tensions in fragile Lebanon that played host to a brutal war among religious sects between 1975 and 1990.
Supporters of Hezbollah clashed with followers of the hardline Sunni preacher in various parts of the country, including the port city of Sidon and the northern city of Tripoli.
Last week, Assir had called on his supporters to fight Hezbollah in Lebanon. He also said that the Lebanese army forces were on the side of the Shia militant group and Iran.
Lebanese armed forces stepped in to quell the fighting in the last few days and have found themselves in conflict with Assir's supporters.
Sunday's fighting comes after the army arrested a supporter of Assir at a checkpoint.
Militia members later surrounded the checkpoint and opened fire causing clashes throughout the afternoon.
Gunfire and burning tires layed by supporters of Assir was also reported in Tripoli, Lebanon's second largest city and the site of intense fighting between Alawites and Sunnis.
It is unclear if power has been restored to the country after fighting disrupted the electrical grid.
The video below shows Sunni cleric Ahmed al-Assir who has called for Lebanese people to fight against Hezbollah: