"He will be returning to [South Africa] once his doctors have completed their treatment," a statement from the Jacob G Zuma foundation continued.

The news comes a day after Zuma, 81, lost a case at the Constitutional Court, where he had tried to overturn a ruling that he must return to prison.

The former president left for Russia last week on a commercial flight, the foundation's spokesman Mzwanele Manyi said.

He has gone to Russia before for treatment, including in 2014 after he was allegedly poisoned.

On Thursday, the Constitutional Court ruled that Zuma had been granted medical parole unlawfully.

He was given parole by the former head of the prison service, Arthur Fraser, who is regarded as an ally of the former president.

Zuma was released in September 2021 after serving less than eight weeks of a 15-month jail sentence.

He had been convicted of contempt, after refusing to co-operate with anti-corruption enquiry during his term in office.

The prisons department has said it is studying the constitutional court’s judgement and will comment after seeking legal advice.

The main opposition Democratic Alliance (DA) has welcomed the court's ruling, saying that it confirms that Zuma "belongs in jail".