Güncelleme Tarihi:
At least 30 people were wounded, two of them seriously, by the bomb, which was planted either inside the bus or beside it and exploded in a busy district of Lebanon's second largest city.
The Red Cross ferried casualties from the site of the blast.
No one has claimed responsibility for the attack in the region which has seen both sectarian fighting and clashes between the army and Islamist militants.
At least 22 people have been killed in Tripoli in recent months in fighting between Sunni and Alawite gunmen in violence linked to lingering political tensions in Lebanon.
Lebanese security forces fought Sunni Islamist militants in Tripoli last year at the start of a insurrection by the al Qaeda-inspired Fatah al-Islam group, which was based at the nearby Nahr al-Bared Palestinian refugee camp.
The army lost 170 soldiers in the fighting.
A new national unity government, formed as part of a deal aimed at defusing the country's crisis, won a vote of confidence in parliament on Tuesday.
Lebanese President Michel Suleiman, who was army chief during the Nahr al-Bared fighting, is scheduled to visit Damascus later on Wednesday to meet Syrian President Bashar al-Assad.
Photo: AFP