The Mozambican authorities say three people are under police detention for their alleged involvement in trafficking of human body parts.
By Jose Tembe
BBC News, Maputo
The case involves this week's murder and mutilation of seven women and a child in Cabo Delgado province.
Murder, mutilation and exhuming human bones for witchcraft have become a common practice, particularly in the country's northern and central regions.
Items are sold in neighbouring Malawi, South Africa and Zimbabwe.
Lazaro Mathe, governor of Cabo Delgado, says the criminals kill their victims and extract genital parts apparently for witchcraft.
He said three people suspected of involvement in the crime are under police custody.
The Cabo Delgado provincial boss has called on the people of Mocimboa de Praia to remain calm, adding that the situation would soon be under control.
This is not the first time that murder cases of people for the extraction of body parts has occurred in Mocimboa da Praia and elsewhere in the province.
The first case was reported last year and two people were detained for allegedly killing nine people. But the police later released one of them for unexplained reasons.
This infuriated the local people who caught and killed the suspect after his release.
The governor describes the phenomenon as worrisome and promises to wage a sustained battle to crack down on it.
Murder and trafficking of human beings and parts have been reported in many parts of Mozambique.
In a recent incident, two young men were detained in northern Niassa province in possession of huge quantities of human bones ready to sell in Malawi.
This has prompted the Mozambican cabinet to enact a bill against the trafficking of humans for body parts to be discussed and approved in the country's parliament this month.