The tour - which also included Senegal and Zambia - comes as Washington faces growing competition in the region with Russia and China.

South Africa has recently taken over the chair of the Brics economic group - made up of Brazil, Russia, India, China and South Africa - which was set up as a counterweight to US global dominance.

While in South Africa, Ms Yellen is expected to push President Cyril Ramaphosa to pursue plans for a gradual transition away from a heavy reliance on coal to cleaner energy.