CAPE TOWN (Reuters) - Jailed former South African president Jacob Zuma has undergone unspecified surgery and remains in hospital with more operations planned, prison authorities said on Sunday.

       Zuma, serving a 15-month sentence in Estcourt prison for contempt of court, was sent to a hospital outside for observation on Aug. 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.

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

       Last week, a high court postponed his corruption trial to Sept. 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 Aug. 20.

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

       Zuma, whose jailing last month ignited looting and unrest, faces charges with co-accused, French defence firm Thales, over a $2 billion arms deal corruption case that led to his sacking as South Africa's deputy president in 2005.

       Zuma and Thales have denied the allegations.

       (Reporting by Wendell Roelf; Editing by Andrew Cawthorne)