Several women were among those killed in Sunday’s roadside explosion that hit a minibus carrying passengers some 36km southeast of the coastal city.
The victims are said to be farmers.
Mohamed Hasan, who saw the blast, said he believed civilians were killed in error.
He saw a Somali military vehicle pass the scene of explosion.
“I saw charred bodies of bodies shortly after the blast. I think the target of the attack was the military soldiers,” he told Al Jazeera.
The bus which was blown up had been heading to Balad town in Middle Shabelle region, according to Harun Osman, a local resident.
No group has claimed the responsibility for the explosion but al-Shabab has carried out similar attacks in and around the capital in recent months.
According to an Al Jazeera tally, since the start of this year, more than 20 explosions have targeted Mogadishu, killing at least 500 people and injuring more than 630.
Sunday’s attack followed the October 14 blast in which at least 358 people died and more than 400 were injured.
The Somali government blamed the October 14 blast on al-Shabab, but no group has claimed the massacre.