A United Nations watchdog has expressed concern over Britain's handling of hundreds of African children who are brought to the UK to undergo brutal voodoo rituals.

The United Nations Committee on the Rights of the Child (CRC) has urged the British government to address the scourge of children kidnapped from Africa for the purpose of cruel religious rituals and slavery.

Although the police have recorded scores of such cases, the conviction rate is low, says the watchdog.

"We're concerned about reports that hundreds of children have been abducted from their families in Africa and trafficked to the UK, especially London, for religious rituals," said the chief of the UN Committee Kristen Sandberg, reports AFP.

"They are used in so-called voodoo rituals, and are also raped and sexually abused. The number of convictions is extremely low," said Sandberg, who heads the 18-member committee monitoring the proper implementation of child rights according to international treaties.

Following a hearing with the UK officials last month, the final report has been released which says the UK should bolster the law-enforcement agencies and judiciary in order to "prosecute trafficking of children for labour, sexual and other forms of exploitation, including for religious rituals".

In the last decade, several cases involving African nationals victimised by witchcraft rituals have come to light prompting the UK government to launch a campaign against faith-based child abuse in 2012.