The US Embassy in Pretoria on Tuesday advised its citizens to be on heightened alert against attack, saying extremists may target American interests in the country.
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"At this stage we have found no imminent danger or threat to the country or the US interests," said Brian Dube, spokesperson for the ministry of state security.
"But we can't dismiss the threat, as we realise that we are dealing with a serious global phenomenon that no one is immune from," Dube told AFP.
He declined to reveal if any measures had been put in place to boost security around US diplomatic offices or businesses since the alert was issued.
The Americans were "very worried about certain individuals who might be a danger", Dube told eNCA television.
The information had been followed up and the conclusion had been reached that there was no immediate threat and "there is no need to panic", he said.
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The US embassy issued a general security alert last week ahead of the September 11 attacks anniversary, but the warning on Tuesday appeared to signal a new level of concern.
There has been no indication of whether the "individuals" of interest to the US are South African nationals or foreigners.
South Africa has escaped the militant attacks seen in several other African countries.
Dube said the local law enforcement agencies "will continue monitoring the situation".
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