The explosion occurred at the crossroads in Mogadishu's Heliwaa district on Monday evening, the Somali National News Agency reported, citing local police. All the victims were on a minibus or a motorcycle at the time of the blast.
Somali security forces have launched an investigation into the incident, the report said.
The radical Islamist group al-Shabaab is affiliated with the al-Qaeda* terrorist group. Its militants fight Somalia's central government and sabotages UN humanitarian operations in the country.
*terrorist organizations banned in Russia and many other countries