The embassy said the warning was issued after ISIS called on its militants to "carry out terrorist attacks globally during the upcoming month of Ramadan."
The U.S. State Department updated a worldwide caution in March, saying ISIS and other terrorist groups continue to plan attacks in many areas of the world. The caution did not specifically mention South Africa.
In Germany Thursday, three Syrian men were arrested on suspicion of planning an attack that was ordered by ISIS. The German attorney general's office said the men wanted to attack the old town in Dusseldorf in western Germany with suicide bombings, guns and explosives.
Attacks claimed by ISIS left 32 people dead in Brussels on March 22, and 130 people were killed in Paris on November 13 in a series of attacks by several ISIS operatives.