South Africa's powerful trade union federation Cosatu, a key coalition partner of the ruling ANC, on Tuesday called for embattled President Jacob Zuma to resign following an unpopular cabinet reshuffle.

Union general secretary Bheki Ntshalintshali said it was time for Zuma to "step down" following his purge of cabinet critics, which included the removal of the respected former finance minister, Pravin Gordhan. His sacking contributed to a credit ratings downgrade to junk status on Monday by Standard & Poor's.