Denis Goldberg said his friend Nelson Mandela looked better than expected.
Two leading South Africans have called for an end to a bitter row among members of Nelson Mandela’s family over the reburial of three of his children.
Deputy President Kgalema Motlanthe said he hoped the public dispute could be resolved in a “dignified manner”.
Archbishop Desmond Tutu pleaded with the family not to “besmirch” Mr Mandela’s name with their squabble.
President Jacob Zuma has meanwhile denied reports that Mr Mandela, 94, was in a vegetative state.
South Africa’s first black president has spent the past four weeks in a Pretoria hospital with a recurrent lung condition.
“Madiba remains in a critical, but stable condition. The doctors deny that the former president is in a vegetative state,” said a statement from Mr Zuma, who visited Mr Mandela on Thursday.
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The statement came after court papers filed on behalf of Mr Mandela’s eldest daughter, Makaziwe, on 26 June said his health was “perilous” and that he was “assisted in breathing by a life-support machine”.
A lawyer has told the BBC this document was never read out in court.
Subsequent court papers seen by the BBC also on behalf of Makaziwe Mandela, do not mention that her father was in a “vegetative state”.One of Mr Mandela’s friends and fellow former prisoners, Denis Goldberg, who visited the anti-apartheid icon on Monday, also said he was responsive but was prevented from speaking because he had tubes in his mouth.
“I’m quite satisfied he was responsive to what I was saying,” he said.
The BBC’s Dr Smitha Mundasad says doctors would only diagnose a vegetative state if a patient was unaware of their surroundings and could not speak or respond to commands.
Patients may, however, breath without assistance, she says.
Crucially, the diagnosis is often only made after four weeks, while a “permanent vegetative state”, which has been mentioned in the court documents, would only be made once the condition was considered irreversible and after at least six months in the UK.
She does, however, note that different countries use different criteria for diagnosis.
Correspondents say there has been a long-running battle over Mr Mandela’s legacy, but that it has intensified as his health has deteriorated.
The feud over the reburial of Mr Mandela’s children is linked to the decision about where he will eventually be buried, as it is thought he would like to interred alongside them.
The legal documents were filed by Makaziwe and several other relatives last week in order to persuade a judge to make a speedy decision over whether to exhume the children.
On Thursday, the three bodies were reburied, following a court order, back in the village of Qunu, where Mr Mandela was brought up and where he is said to want to be laid to rest.
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Earlier, forensic tests confirmed the identity of the bodies which had been exhumed by police from the homestead in the village of Mvezo owned by Mr Mandela’s grandson, Mandla.
An affidavit filed by Mandela family members alleged that Mandla had relocated the graves in 2011 to ensure that his grandfather would be buried in Mvezo, against his wishes.
At a news conference on Thursday, Mandla accused some of his relatives of washing their dirty linen in public and battling for control of his grandfather’s assets.
“In the past few days, I have been the target of attacks from all sorts of individuals wanting a few minutes of fame and media attention at my expense,” he said.
His family rivals were motivated by revenge as he had refused to support their legal case to oust three of Mr Mandela’s aides from companies the ex-president had set up, Mandla added.
Later, Deputy President Motlanthe criticised the behaviour of Mr Mandela’s family on a radio chat show in Johannesburg.
“It’s all very sad, but we’ve got to continue keeping the family and Madiba in our prayers and hope, continue to hope, that Madiba will recover and also that the family will manage its own affairs in a dignified manner,” he said.
Archbishop Tutu, who, like Mr Mandela, won the Nobel Peace Prize for his role in the struggle against white minority rule, appealed to the family to overcome their differences.
“Please, please, please may we think not only of ourselves? It’s almost like spitting in Madiba’s face,” he said in a statement.
“Your anguish, now, is the nation’s anguish – and the world’s. We want to embrace you, to support you, to shine our love for Madiba through you. Please, may we not besmirch his name?”