Kidnappers have freed the 82-year-old mother of Nigerian Finance Minister Ngozi Okonjo-Iweala, five days after she was taken from her home in Nigeria, a senior security official said.

"She has been released now by her captors and she is at home," said the source, who had confirmed Kamene Okonjo's kidnapping on Sunday.

It was not clear if the abduction of Mrs Okonjo was political or for financial gain.

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Nigeria's army said on Thursday that soldiers had arrested 63 people in raids conducted during the search for Mrs Okonjo.

Kidnapping is rife in Africa's top oil producer and tends to surge in December, when the criminals need money for year-end festivities.