A high court in South Africa's administrative capital Pretoria has ruled that a previous decision to place former President Jacob Zuma on medical parole was unlawful and ordered that he should return to jail.

"It is declared that the time [Zuma] was out of jail on medical parole should not be counted for the fulfilment of [Zuma's] sentence of 15 months imposed by the Constitutional Court," the court ruled on Wednesday morning.