CAPE TOWN, Aug 15 (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. read more "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. read more 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. read more Zuma, whose jailing last month ignited looting and unrest, faces charges with co-accused, French defence firm Thales (TCFP.PA), 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.