Gunmen killed an Alawite in Lebanon's second city Tripoli on Wednesday, triggering renewed sectarian clashes which killed an 11-year-old boy in a Sunni Muslim neighbourhood, a security source said.
The slain man's car crashed after the shooting, killing a woman bystander, and injuring her son and a street vendor, the source said.
Hours afterwards, armed exchanges erupted between neighbouring Alawite and Sunni districts of the northern port city, where an uneasy calm had lasted just days after a previous round of fighting.
Tripoli has been rocked by repeated bouts of violence linked to the conflict in neighbouring Syria, pitting its Sunni majority, who largely support the rebels, against the Alawite minority, who back their coreligionist President Bashar al-Assad.
"An Alawite employee of Tripoli city council was shot dead by two men on a motorbike who chased his car as he drove home after work," the security source told AFP.
"The car went out of control after the shooting, and crashed into a vegetable cart. A woman was standing there with her child. Both were wounded, and she died of her injuries soon afterwards," he added.
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"The son's hand was broken, as was the cart vendor's leg."
Hours after the shooting, clashes erupted on the dividing line between the city's mainly Sunni Bab al-Tebbaneh and mainly Alawite Jabal Mohsen districts.
A rocket killed an 11-year-old boy and wounded another person in Bab al-Tebbaneh, the security source said.
A similar deadly attack on a Sunni earlier this month by gunmen on a motorbike sparked 13 days of clashes between the rival neighbourhoods that killed 27 people.
Tensions between the two districts go back decades but have been exacerbated by the three-year-old conflict in Syria.
In December, Human Rights Watch said a government security plan for Tripoli "should specifically include measures to protect Alawite residents and their property."
Alawites make up 11 percent of the city's population. Sunnis account for 80 percent.