Jailed former South African President Jacob Zuma has undergone unspecified surgery and remains in hospital with more operations planned, prison authorities said.

Zuma, serving a 15-month sentence in Estcourt prison for contempt of court, was sent to a hospital outside for observation on August 6, days before the start of a corruption trial he has thus far avoided.

“Mr Zuma underwent a surgical procedure on Saturday, 14 August 2021, with other procedures scheduled for the coming days,” prison spokesman Singabakho Nxumalo said in a statement on Sunday.

There was no word on a potential discharge date for Zuma, who in July asked the country’s top court to reverse his imprisonment, saying it was unjust and might kill him if he catches COVID-19.

Last week, a high court postponed his corruption trial to September 9 after his hospitalisation. It is unclear what medical condition ails Zuma and his legal team was ordered by the judge to produce a medical report by August 20.

The prosecutors may appoint a doctor of their choice to assess whether Zuma is fit to stand trial.

The former president is jointly accused with French arms firm Thales and is facing 18 charges, including corruption, money laundering, and tax evasion racketeering linked to a $2.5bn arms deal in the late 1990s.

Zuma and Thales have denied any wrongdoing.

Charges against Zuma were dropped in 2009 by former National Prosecuting Authority head Mokotedi Mpshe weeks before he was elected president.

They were, however, reinstated in 2018, marking one of the longest-running legal battles in the country.

Zuma is currently serving a 15-month sentence for contempt of court and his detention led to riots and looting. More than 200 people were killed in the riots that caused damage estimated at billions of South African rands.