Nigeria's Finance Minister Ngozi Okonjo-Iweala says her mother's kidnappers demanded her resignation.In her first public comments since her 82-year-old mother's release, Mrs Okonjo-Iweala said the kidnappers mentioned her battle against a multi-billion dollar fuel scam.Kamene Okonjo was freed on Friday after gunmen held her for five days.Mrs Okonjo-Iweala pushed a government policy to end fuel subsidies in January, sparking a nationwide strike.The government then agreed to partially restore the subsidy.Kidnapping is common in southern Nigeria, where it is a lucrative criminal enterprise.'No backing down'She said her mother, a retired professor, was held without food or water."The kidnappers spent much of the time harassing her. They told her that I must get on the radio and television and announce my resignation," Mrs Okonjo-Iweala said in a statement.Earlier this year, a parliamentary investigation found that a scam linked to the subsidy cost the country $6.8bn (£4bn).Kamene Okonjo was kidnapped from her home in southern Nigeria's Delta state on 9 December.On Friday, officials said she had been released and that her abductors had dropped her off near her home.It is not clear whether a ransom was paid to secure her release.Mrs Okonjo-Iweala, 58, did not answer any questions after making her statement.She is an internationally respected economist who has led a high-profile campaign to clean up corruption in Nigeria.The finance minister said the kidnapping would not change the policy of President Goodluck Jonathan's government."For marketers whose transactions are proven to be fraudulent, the position of the Jonathan government is also clear: We cannot and we will not pay," she said."We will not back down on this. We will continue to stand firm."Last week, finance ministry spokesman Paul Nwabuikwu said that Mrs Okonjo-Iweala had been threatened recently.Officials said Kamene Okonjo had probably been released because her abductors were under pressure, following a series of raids by Nigeria's security forces to hunt them down.