The Lebanese army said the bomb went off Thursday evening in the Ruwaiss neighborhood as people were returning home from work for the day.
Ruwaiss is considered a Hezbollah stronghold, The Daily Star reported.
Authorities were investigating whether the bombing was a suicide attack, security sources, whose names were not reported, told the newspaper.
A group referring to itself as Brigade of Aisha, or the Mother of the Faithful, claimed responsibility for the attack. The group was previously unheard of and possible affiliations with other groups were not reported.
Nasrallah said Israel was behind the attack, perhaps in retaliation for a Hezbollah attack on Israeli soldiers who had crossed the border into Lebanon, the Star said.