Kenya has urged former anti-corruption official John Githongo to submit a tape which he says implicates a minister in attempts to slow a corruption inquiry.
Government spokesman Alfred Mutua said Nairobi wanted to assess the tape's authenticity before passing it on to Kenya's anti-corruption commission.
Mr Githongo has told the BBC the tape was made during his talks with Kiraitu Murungi, who is now energy minister.
Mr Murungi - who was justice minister at the time - denies any wrongdoing.
Mr Githongo also says he told President Mwai Kibaki about the corruption, but the president failed to act.
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President Kibaki on Thursday pledged that he and his government would take "expeditious and decisive" action in the fight against corruption.
His remarks came as several Kenyan lawmakers prepared to travel to London to interview Mr Githongo - now in exile in Britain - over wider allegations of graft he has made against senior government members.
Bogus companies
On the tape, a man Mr Githongo says is the minister is heard telling him that the loan is owed to a businessman with links to powerful politicians and that if he goes slow on his investigation the businessman will also go slow.
"The minister of justice was telling me that if I eased off my enquiries then my father's loan matter would be made to go away," Mr Githongo said.
Mr Murungi would not be interviewed but denies wrongdoing.
Mr Githongo says government money was being paid to companies that did not exist or to others which were massively overpricing their contracts.
The scandal, known as the Anglo Leasing affair, has cost the Kenyan exchequer millions of dollars, according to Mr Githongo's investigations.
He believed the finance was being given to business figures close to the government, who were then re-directing some of it back to the ruling elite for political campaigning.
The Kenyan government has not reacted officially to Mr Githongo's latest allegations.
Mr Githongo now lives in the UK and has said he fears for his safety if he were to return to Kenya.