The incident occurred in Hawa Abdi village, less than 10 kilometers (6.2 miles) from the Somali capital Mogadishu.
Lower Shabelle Governor Mohamed Ibrahim Barre told reporters the victims were killed by members of the al-Qaeda affiliated al-Shabaab group.
”Al-Shabaab fighters attacked street cleaners in Hawa Abdi, killing nine people, including six women. This is an evil attack by al-Shabaab, and really, this a massacre,” Barre said.
The victims, who were all civilians, came under attack as a sanitation campaign was underway in the village organized by the administration, he added.
Barre called on the Somali people to unite in the fight against al-Shabaab.
Although Somali officials blamed al-Shabaab for the attack, no group has yet claimed responsibility.
The incident took place on the same day that U.S. Africa Command (AFRICOM) announced that an airstrike had killed 35 al-Shabaab militants in Hiran province in central Somalia.
The airstrike was conducted 20 miles east of the city of Beledweyne on Sunday.
The bombing was part of an effort toward targeting al-Shabaab and reducing its strength in the region as well as supporting the Somali National Army.
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