South Africa's president has reprimanded defence minister Nosiviwe Mapisa-Nqakula and docked her pay for three months for taking a delegation to Zimbabwe on an air force plane, his office said.

The opposition Democratic Alliance had accused Mapisa-Nqakula of misusing state resources by letting the group from the ruling African National Congress (ANC) travel with her to Harare in September.

The presidency said late on Saturday Mapisa-Nqakula had been on an official trip. But her decision to let the delegation - who were travelling to Zimbabwe on unrelated business - join her on the flight had been an "error of judgement".

It said President Cyril Ramaphosa had told Mapisa-Nqakula in a letter that this was not in keeping with her responsibilities as a cabinet minister. The minister had been given a formal reprimand, a "salary sacrifice" had been imposed on her for three months from November 1 and she would have to make sure the ANC reimbursed the state for the costs of the flight, the presidency added.

A defence ministry spokesman did not immediately respond to requests for comment from the minister. Mapisa-Nqakula herself did not immediately respond to a message sent on LinkedIn.

Ramaphosa has pledged to clean up the ANC's reputation after a decade of scandals under his predecessor Jacob Zuma.