With the clashes intensifying, another 47 people have been wounded since gun battles broke out on Monday while an interview with Syrian President Bashar al-Assad was being aired on television.
“Fierce clashes broke out once again last night pitting gunmen from [the majority Sunni, anti-Assad] Bab al-Tabbaneh against [the Alawite, pro-Assad] Jabal Mohsen neighbourhoods,” the official, who spoke to AFP news agency on condition of anonymity, said on Friday.
“Fighting raged until 5am [02:00 GMT], and machine guns, rockets and mortar rounds were used,” he said, adding that one person was killed while an army officer and a soldier were among 10 wounded.
The latest fighting “was the fiercest in terms of the intensity of fire and the types of weapons used,” said the official.
The seven killed this week were residents of Bab al-Tabbaneh and Jabal Mohsen.
Many residents of the two impoverished neighbourhoods, which have suffered frequent rounds of fighting ever since the outbreak of conflict in neighbouring Syria in 2011, have fled their homes for other parts of the city.
Schools and universities have been closed in Tripoli since mid-week.
Lebanese President Michel Sleiman said on Thursday evening that he had ordered security forces to restore order as soon as possible.
Lebanon is deeply divided into pro- and anti-Damascus camps.
The division has widened since the Lebanese Hezbollah group admitted in May it was sending fighters into Syria to support Assad’s troops.
Small armed Sunni organisations have also sent men across the border to fight alongside the rebels.
Lebanon was dominated politically and militarily by Damascus for 30 years until 2005.