By Tom Esslemont

BANGUI (Thomson Reuters Foundation) - Rebels in Central African Republic have kidnapped, burnt and buried alive "witches" in public ceremonies, exploiting widely held superstitions to control areas in the war-torn country, according to a leaked United Nations report.

The report by U.N. human rights officers, seen exclusively by the Thomson Reuters Foundation, contains graphic photographs of victims tied to wooden stakes being lowered towards a fire as well as the charred torsos of those subjected to the ritual.

The torture took place between December 2014 and early 2015 under instruction from leaders of the mainly Christian "anti-balaka" militia that has been fighting Muslim Seleka rebels across the country for more than two years, said the report.

Central African Republic was plunged into sectarian violence when Muslim rebels briefly seized power in the largely Christian country in March 2013, with escalating violence on both sides creating lawlessness nationwide outside the capital Bangui.

Internationally-backed presidential and parliamentary elections are due to be held on Dec. 27 after repeated delays to replace a transitional government but there are widespread concerns of more bloodshed in the run-up.

While belief in witchcraft is common throughout Africa, U.N. researchers said it appeared Christian rebels had used these superstitions to intimidate, extort money and exert authority over lawless areas.

"Sorcery is firmly entrenched in (Central African Republic) and ... the absence of state authority creates a breeding ground for a sort of popular justice twisted by anti-balakas to its benefit," said the researchers.

The report, produced by a team working for the U.N.'s stabilisation mission known as MINUSCA, said 13 attacks against victims aged between 45 and 70 are said to have taken place near Baoro in Nana-Mambere, one of 14 prefectures in the country.

Nana-Mambere in the country's south west has been ravaged by violent clashes between rival rebel groups with U.N. peacekeeping forces unable to restore calm.

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The report identifies three leaders of the anti-balaka faction in Nana-Mambere present during the alleged torture sessions but attempts by the Thomson Reuters Foundation to reach them did not elicit a response.

"FASTENED LIKE A CHICKEN"

In one incident, a local Christian clergyman, who had scars across his body, said he tried to intervene as he witnessed a man being buried alive after being condemned as a witch for apparently admitting to killing 150 people.

"The clergyman was threatened at knifepoint for trying to intervene in matters that did not concern the church," an eyewitness was quoted as saying in the report.

Victims were ordered, sometimes at gunpoint, to pay between 20,000 and 50,000 Central African Francs ($30 to $80) in bribes to avoid being tied up or burned. Nearly two thirds of people in CAR live on less than $1.90 a day, according to World Bank data.

"Anti-balakas are extorting huge sums from their victims, in exchange for their freedom," the U.N. document said.

Witchcraft is still punishable by law in Central African Republic and jail terms are commonly handed out as punishments with some reports saying half of the country's jails are taken up with those accused of witchcraft.

In September 2010, the High Court in the capital Bangui found four people, including two children aged 10 and 13, guilty of witchcraft and charlatanism, Amnesty International reported.

The recent violence has left the main jail in Bangui almost completely empty but just outside the capital at Bimbo women's prison, five of 18 inmates are held on charges of witchcraft.

"I was accused of killing my husband through witchcraft," said Christelle Ouamanga, 26, in an interview with the Thomson Reuters Foundation from the cell she shares with five others.

Ouamanga, nursing her seven-month-old son Dieupuissant in jail, denies murder but said her husband's family accused her of sorcery after his death that she blames on lung disease.

Father Aurelio Gazzera, a missionary working with Catholic charity Caritas in western Central African Republic, said the concept of witchcraft was "aggravated during moments of crisis" such as the ongoing violence.

"Punishment (of those deemed witches) is used as a means by an armed group to impose its authority," said Gazzera, whose charity is one of the few to operate in Nana-Mambere, around 300 km (200 miles) northwest of the capital.

Interim justice minister Dominique Saïd Panguéndgi, who like all members of the transitional administration is barred from running in the upcoming elections, said judicial reform regarding witchcraft had been slow and not deemed a priority.

"Witchcraft is a question of belief, so we need to train magistrates," he said in his office in Bangui. "But at least the debate (about witchcraft) has begun."

(Reporting By Tom Esslemont, Editing by Ros Russell and Belinda Goldsmith; Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women’s rights, corruption and climate change. Visit www.trust.org)