'There was no meeting of minds . . . the African National Congress (ANC) said it will reserve the right to criticise the police,' the source said.
Earlier, Mr Mandela was in Katlehong, the township near Johannesburg where more than 130 people have died in political violence since the weekend. Addressing a rally at the soccer stadium, he bitterly attacked the white-led security forces, saying they let blacks die like flies.
When he arried at the stadium, a message awaited him, scribbled on the table next to his microphone. 'No peace. Do not talk about peace. We've had enough. Please Mr Mandela, no peace. Give us weapons. No peace.' The message captured perfectly the mood of the 10,000 ANC supporters present.
At least 300 people have died in the area since 1 June, the conflict resting fundamentally between Inkatha Freedom Party supporters operating out of the single-men's hostel and the rest - residents of a township with the highest number of signed-up ANC members in the country.
In such a climate, it came as a surprise yesterday when, upon Mr Mandela's appearance at the stadium, anger and gloom instantly gave way to jubilation. The delirium suggested the ANC had just won a general election.
The sky, however, told a different story. Army helicopters circled overhead. And outside the stadium large numbers of troops and armoured vehicles kept watch. It was in sombre mood that Mr Mandela finally stepped up to the microphone for, it transpired, he had come not to praise ANC supporters in Katlehong but to scold them.
But first he scolded the powers that be. 'The first big problem is the unwillingness of the government, the police and the South African Defence Force to protect our people . . . To them the lives of black people are cheap. It is as if flies had died.'
The crowd responded appreciatively. Less so to his next remarks. 'There are times now when our people participate in the killing of innocent people. It is difficult for us to say when people are angry that they must be non-violent . . . But the solution is peace, it is reconciliation, it is political tolerance.'
Accordingly, he suggested, they should recognise that not all hostel-dwellers were criminals. They should be allowed out of the hostel to go to the shops, to visit relatives - freely. The crowd murmured. Some jeered.
'No,' Mr Mandela said. 'We must accept blacks are fighting each other in our townships. So the task of the ANC is to unite black people as well as whites . . . But the National Party of De Klerk, the police, the army are also involved and that makes the task more difficult.' The crowd warmed to him again.
Most of Mr Mandela's speech was off the cuff, as if he were engaging in a dialogue with his supporters. Winning them over, shocking them, responding to their shock. His boldest message he delivered at the end of his one-hour speech.
'We must accept that responsibility for ending violence is not just the government's, the police's, the army's. It is also our responsibility . . . We should put our own house in order. If you have no discipline you are not freedom fighters. If you are going to kill innocent people you don't belong to the ANC.
'Your task is reconciliation. You must go to your area and ask a member of Inkatha: why are we fighting?' The crowd turned again. They did not want to hear this. 'Listen to me] Listen to me]' he cried above the din. 'I am your leader. As long as I am your leader I am going to give leadership. Do you want me to remain your leader?' Chastened, alarmed, they bellowed back, 'Yeees]'