The Nelson Mandela Foundation says South Africa's scandal-tainted President Jacob Zuma must go "sooner rather than later" and that any delay would lead to violent conflict.

The non-profit group on Tuesday adds that Zuma's departure would not be enough to address deep-rooted corruption in one of Africa's most developed countries.

The organization promotes the legacy of South Africa's anti-apartheid leader and first black president.

The group first called for Zuma to resign more than a year ago.

The president has been enmeshed in a series of scandals but denies wrongdoing. Many members of the ruling African National Congress party have turned against him. They worry he hurts the party ahead of 2019 elections.

Pressure is growing as Zuma is set to deliver a state of the nation address on Thursday.