South Africa's state security agency on Friday said it had found no evidence that Iran was plotting to assassinate the US ambassador to Pretoria, Lana Marks.
A US media report, quoting unnamed officials, earlier this week said that Iran was planning to kill the US ambassador to South Africa ahead of the US presidential election in November.
Such a plot would act as a revenge attack after President Donald Trump decided to kill Qassem Soleimani, a powerful Iranian general.
"At present, the information provided is not sufficient to sustain the allegation that there is a credible threat against the United States Ambassador to South Africa," State Security Agency spokesman Mava Scott said in a statement.
"Such plots of assassination against diplomats are viewed in a very serious light and Her Excellency, Ambassador Marks has been assured of our commitment in this regard."
On Monday, Iran's foreign ministry denied the report as "baseless" and part of "repetitive and rotten methods to create an anti-Iranian atmosphere".
Relations between Washington and Tehran have been tense ever since the Islamic revolution of 1979.
They have deteriorated sharply since Donald Trump unilaterally pulled out of a landmark international nuclear deal with Iran in May 2018 and reimposed crippling sanctions.
The South African state security agency said officials had requested additional information from the US government and urged "everyone to remain calm".