The Democratic Alliance (DA), South Africa's biggest opposition party, on Thursday threatened to approach the courts should African National Congress (ANC) President Cyril Ramaphosa offer the country's head of state immunity from prosecution on corruption charges.

In a statement, the party said it was "not a stretch" to speculate that a deal for immunity was at the centre of talks between Ramaphosa and State President Jacob Zuma over the latter's future.

"Should Ramaphosa choose to offer or purport to grant Zuma immunity from prosecution, the DA will not hesitate to go to court. We cannot condone or allow Zuma to escape accountability for breaking his oath of office and putting his friends and family above the best interests of the people of South Africa," the party said.

"It is incomprehensible that immunity would even be considered given the devastating impact Zuma’s presidency has had on the country. It also shows that the ANC under Ramaphosa is the very same ANC it was under Zuma."

Zuma has 783 counts of fraud, corruption, money laundering and racketeering - related to the country's arms deal - hanging over his head.

He was meant to deliver the state-of-the-nation address on Thursday evening, but this was postponed as his negotiations with Ramaphosa continued after party heavyweights called on him to resign. The president has however failed to step down, prompting talks between him and Ramaphosa over the transition.

Zuma is also accused of helping his friends and family benefit from lucrative government contracts.