The police and armed forces in South Africa announced on Friday that security would be reinforced this weekend following an alert launched by the US embassy in Pretoria last Wednesday.
The alert warned of a possible attack this Saturday in a suburb north of Johannesburg.
South Africa hosts four major events this weekend including the coronation of King MisuZulu Zulu in Durban, an event attended by President Cyril Ramaphosa.
Johannesburg hosts a gay pride event, there is also a rugby match in Pretoria and the football derby in Soweto.
Nigeria's capital, Abuja,is also under a security alert. Since Sunday that the embassies of the United States, Britain, Australia and Canada have been alerting to the "high" probability of an attack in the capital.
On Friday, the Nigerian government said it had beefed up security and called for the public to remain vigilant but calm.
Government troops are fighting jihadist insurgents mostly in the northeast, though there are small cells in other parts of the country.
Counting underway in Nigerian vote for new governors
Nigeria electing governors after disputed presidential vote
US Secretary of State Blinken visits Niger on Africa tour
Go to video
Nigeria: Deadly fighting between rival jihadist groups
Go to video
Morocco: Suspected jihadists arrested after police officer's murder
After the Nigerian presidential election, the struggle for Lagos intensifies