The head of Nigeria's main anti-corruption agency on Monday said he wanted former oil minister Diezani Alison-Madueke to be extradited to face trial because a corruption probe against her in Britain was taking too long.Alison-Madueke, who served under president Goodluck Jonathan and was the first female head of OPEC, was arrested in London in October 2015 as part of a probe into global corruption.She has been on bail ever since, and been linked to a string of money laundering, bribery and asset recovery cases in Nigeria, Italy and the United States.The claims are that billions of dollars were siphoned from oil deals and state accounts, including to pay for properties in exclusive areas of Lagos and London.The former minister, 57, denies the charges.Nigeria's government has previously appeared happy to have Alison-Madueke potentially face trial in Britain.A judge in Lagos in November last year even accused her of seeking to "avoid justice" after her lawyers applied to have her name attached to a fraud case. Nigerian court cases frequently last years and there is criticism about corruption in the judiciary. But the chairperson of the Economic and Financial Crimes Commission (EFCC), Ibrahim Magu, said the British probe began even before he was appointed and she had still not been charged."It is very unreasonable that she is not being tried there," he told a news conference in the capital, Abuja."That's why I say, if you cannot prosecute her, bring her here. We will prosecute her... We cannot wait endlessly like this. I think three years and above is sufficient to take her to court."He added: "There's no prosecution, nobody is prosecuting her there. That's why I said let us initiate (an) extradition process."There was no immediate response from the interior ministry in London, the National Crime Agency or the British mission in Abuja.Nigerian President Muhammadu Buhari was elected in 2015 on a promise to root out endemic corruption and end impunity in Africa's most populous nation.That included reforming the notoriously opaque Nigerian National Petroleum Corporation (NNPC) which Alison-Madueke oversaw.But three years on, and as he seeks re-election at polls in February next year, he has yet to secure a big-name conviction, after claims he has targeted political opponents.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.