The mother of Nigeria's finance minister has been released unharmed by kidnappers five days after she was abducted from her home in the southeastern part of the country.

The 82-year-old woman, Kamene Okonjo, is the mother of Ngozi Okonjo-Iweala, who has twice served as the country's finance minister and also worked at the World Bank as a director.

"She has been released now by her captors and she is at home," an unnamed security official told Reuters.

On Thursday, the Nigerian army said it had arrested more than five dozen people in connection with the investigation into Kamene Okonjo's disappearance.

It is unclear if a ransom was paid, or if politics was the motive foir the adbuction – finance minister Okonjo-Iweala had aggressively sought to pursue and punish corrupt politicians and businessmen, likely earning many enemies. Her elderly mother, a retired college professor, was also involved in local politics in the Delta.

The Nigerian government has a policy of not paying ransom to kidnappers, however, according to reports, wealthy victim's families often cough up money to pay criminals.

Delta state governor Emmanuel Uduaghan told the BBC that Kamene Okonjo may have been freed because the kidnappers could not face the pressure from the authorities hunting them down.

"The army and police have been on their trail and a lot of raids have been done. I think because of the heat they dropped her off on the highway," he said.

A spokesman for the finance ministry, Paul Nwabuikwu, revealed earlier in the week that Okonjo-Iweala had recently been threatened.

In any case, kidnapping is a multi-million-dollar national industry in Nigeria, particularly in the oil-rich south where Kamene Okonjo was seized.

The British-based crisis management assistance and global security company, Red24, said that Nigeria is one the world's ten most dangerous countries with respect to kidnapping – at least 1,000 kidnappings for ransom are recorded there annually.

BBC noted that kidnappings in Nigeria – frequently of businessmen, atheletes, foreign workers, etc. – have become so routine that they do not even make front page news.

In an advisory to British nationals, the UK Foreign & Commonwealth Office (FCO) warned “there is a threat of kidnapping throughout Nigeria. Kidnappings can be for financial or political gain, and can be motivated by criminality or terrorism.”

Since January 2007, at least 25 British and more than 200 other foreign nationals have been kidnapped in the Niger Delta area alone, FCO stated.

“There is a high threat of kidnapping and other armed attacks targeting oil and gas facilities and workers. This also applies to ships and oil rigs at sea off the coast of the Niger Delta,” FCO added.

Red24 chief executive Maldwyn Worsley-Tonks said that kidnapping for ransom has become a growing, global threat.

“The crime, which was once synonymous with Colombia and the wider Latin America region, has spread to more locations across the world, making it a risk that both businesses sending employees abroad and individual travellers cannot afford to ignore,” he said in a statement.