South African President Jacob Zuma.

South African President Jacob Zuma said on Wednesday an anti-corruption watchdog had no right to call for a judicial inquiry into alleged influence-peddling in his government, describing its report as unfair.

The report by the Public Protector watchdog, released on November 2, focused on allegations that businessman brothers Ajay, Atul and Rajesh Gupta had influenced the appointment of ministers.

While stopping short of conclusive findings, it has increased pressure on Zuma by calling for an investigation into whether he, some cabinet members and some state companies acted improperly.

Wounded by the latest in a series of scandals, Zuma, who denies wrongdoing, hit back in a speech to parliament.

"No one, no matter what position they hold, can instruct the president to establish a commission and even tell the process through which it must go... so that's a problem," he said.

"This report has been dealt with in a very funny way. It affected me and many (others). No fairness at all."

The affair has rattled financial markets in Africa's most industrialised economy, which risks credit rating downgrades later this year, and spurred efforts by the opposition to unseat the president.

Zuma said South Africa has done enough to boost growth and avoid a downgrade to junk status, which would raise borrowing costs and deter investment. Growth is expect to be less than 1 percent in 2016. "I believe we have indeed done a lot working together to create favourable conditions for economic growth and to stave off any downgrade," he said.

Zuma said the actions of the nation's banks in cutting off business with the wealthy Gupta family, whose alleged influence over him lay at the heart of the watchdog's report, were "suspicious" and needed to be investigated.

The Gupta family denies seeking influence from Zuma.

"Here there was an action by a number of banks at the same time. It suggests that there is something untoward here. And as government, we wanted to constructively interact with the banks," Zuma said.

Several South African companies, including all four major banks, cut links in April with companies associated with the Guptas.