The tapes were broadcast last night on the cable television channel CNBC, provoking furious denials from Dr Mahathir, who is facing the most serious popular challenge in his 17 years as leader. For the fourth day since they arrested Mr Anwar last Sunday, police failed to produce him in court, and warned of stern action if there was any repeat of this week's demonstrations against Dr Mahathir.
Mr Anwar served for six years as finance minister and later deputy prime minister before being sacked three weeks ago for alleged sexual indecency. He has not been seen by his family or lawyers since his arrest. "My sin was that I wanted to protect truth, justice and the interests of the people. The reason why they are afraid of me is that I know too much about their secrets," he says in the recordings.
For the first time, he named the projects in which he alleges corruption. He said that the construction of a new airport and deals involving the state oil company, Petronas, were "done to maintain the interests of his [Dr Mahathir's] cronies", including his son, Mirzah. He also claimed that members of the ruling United Malay National Organisation siphoned off party money, but that Dr Mahathir ignored the matter when it was brought to his attention.
Kuala Lumpur was calm yesterday, and there has been no recurrence of the disturbances of Sunday and Monday. The latest accusations will have limited impact within Malaysia because they have gone almost entirely unreported.
The Malaysian media is closely monitored by the government and this summer two newspaper editors were sacked for apparently favouring Mr Anwar. In the past few days, the government has launched bitter attacks on foreign reporters, whom it accuses of misrepresenting the situation.
Dr Mahathir responded with sarcasm when the latest allegations were put to him. "Of course, I'm remaining in power because of my cronies and my family, and you are free to air these every half an hour, and you can tell lies to the whole world, and influence the whole world against us ... You can tell lies - go on, I don't care."