The traffickers are said to target the sex organs of children, which are sold to make magic charms.

The nuns from the Sisters Servants of Mary Immaculate order say they have gathered evidence of the trade.

They say they have spoken to victims who managed to escape and photos of dead children with missing organs.

'Orphans targeted'

Ritual murders have been reported in many African countries, as some witchdoctors say using human organs in magic charms makes them more powerful.

These are believed by some to bring financial or sexual success to those who use them.

"We have received some very clear threats," order spokeswoman Sister Juliana told Portuguese radio.

Many Africans believe in traditional medicine

"Several countries are involved in this iniquitous game and the victims are the poor, those who have no voice or defence, or the strength to defend themselves, we are convinced that Nampula is part of an international ring," said Sister Juliana.

She said there have been several attempts to abduct children from the orphanage they run in Nampula.

Mozambican, South African, Brazilian and Portuguese nationals were involved in the ring, she said.

The BBC's Jose Tembe in Mozambique says the government had sent a team of investigators to the area to probe claims of the existence of the network.

The organs are reportedly smuggled into neighbouring Zimbabwe and South Africa.

The Spanish Embassy in Mozambique is also investigating the claims after receiving reports from the nuns, who have lived in the area for 30 years.