A human rights group says it has bought the freedom of more than 1,000 Sudanese slaves, most of them children.

Christian Solidarity International, which paid around $50 a person, has called upon the United Nations to launch an investigation into child slavery in the country.

Children are major targets

The group said it freed 1,050 slaves during a visit to the southern Bahr-El-Ghazal region, between 8 and 13 January.

They paid Arab slave retrievers the equivalent of $52,000 using funds from European and American financial backers.

CSI representatives said the slaves had been subjected to repeated physical and psychological torture.

This included slitting throats, death threats, female genital mutilation and beatings.

They were also forced to convert to Islam and made to do unpaid labour, the Swiss based group said.

But the human rights group warned the government's armed forces were already getting ready for a fresh wave of ''slave raids'' next month in the famine-hit region.

It said fears of such attacks have already prompted large numbers of people to flee their homes to protect their children.

Holy war

Christian Solidarity International, which believes the rescue is the largest in the country's known history, says it has freed 5,066 slaves since 1995.

It is also appealing for a UN investigation into child slavery in Sudan, and urging Unicef to establish a slave-tracing and retrieval program in the country.

CSI says the persecution of Christians has become a hallmark of the country's brutal civil war.

In 1983, the Arab government of northern Sudan instituted strict Islamic law which included black Christians and other non-Muslims of the South.