Investigators in southern Beirut have been combing through the blast site of Thursday's attack that killed six people and injured dozens more.
The pro-Hezbollah area has been targeted several times over recent months.
Some believe the explosion was a retaliation against Hezbollah, fighting alongside forces of Syria's President Bashar al-Assad. But unlike previous bombings, there have been no immediate claims of responsibility.
Al Jazeera's Zeina Khodr reports from southern Beirut.