Witnesses and warring factions involved said the incident occurred at the Sinai checkpoint which lies on the Green Line dividing the city.
They said the deaths and injuries were the result of armed men opening fire on others travelling in a pick-up truck.
Four of the dead were part of a group led by a tribal leader named Bashir Raghi, while the others were manning the checkpoint.
All of the killed and wounded are members of the Abgal sub-clan of the Hawiya clan, which is dominant in the capital.
It was not clear what sparked the confrontation.
No functional government to speak of has existed in Somalia since 1991, the year president Muhammad Siad Barri fled the country amid escalating clan warfare that has ravaged the country ever since.
Despite the formation of a new parliament outside the country, Somalia is still currently split into numerous fiefdoms governed by tribal chiefs.