A spokesman for the South African Presidency has said that earlier media reports that former president Nelson Mandela has been discharged from hospital were "incorrect".
Mac Maharaj said: "Madiba is still in hospital in Pretoria, and remains in a critical but stable condition.
"At times his condition becomes unstable, but he responds to medical interventions."
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Explosives experts were called to the nuclear reprocessing site in Cumbria, to help deal with chemical substances.
The arrests were made on suspicion of producing and disseminating pedophilia content on the internet, the country's Justice Ministry said.
The A4-sized sketch originally went for £75 when it was first sold.