The murder of two toddlers whose bodies were found in a toilet in a township north of Johannesburg has sparked riots with people accusing police of failing to protect them.
The discovery prompted angry protests from residents who looted shops and burned tires in the street.
Police were holding several people for questioning about the deaths of the girls, who were two and three years old and were discovered Tuesday in the Diepsloot area north of Johannesburg after being reported missing at the weekend.
Police are investigating whether they are linked to the death of a five-year-old girl in the same area in September. She had been sexually violated and strangled.
In a separate incident two other toddlers were found dead in Katlehong, east of Johannesburg. Police suspect they were poisoned.
The killings in Diepsloot fuelled angry accusations from residents that police were failing to provide security. Some immigrant-owned shops were attacked, exposing tensions between local community members and residents from other African countries in poor areas of South Africa where there are few opportunities.
Nathi Mthethwa, South Africa's minister of police, urged communities to help police solve crimes such as the killing of the children, saying the government would not tolerate lawlessness in the street.
"We condemn any form of mob justice," he said. "Destroying property, looting shops, cannot be a legitimate form of resolving challenges around policing. "
"These gruesome incidents of extreme torture and murder of our children do not belong to the society that we are continuously striving to build together," President Jacob Zuma said.