The US embassy in Pretoria was evacuated on Tuesday morning, but officials refused to comment on the reason.

Spokesperson Sharon Hudson-Dean said everything was back to normal by 9am, adding that the embassy has a series of routine and non-routine procedures, including regular drills.

"We work closely with South African law enforcement officials," she said.

High security was being maintained at the embassy following last month's security threat.

Although the embassy kept the details of the threat discreet, foreign news agencies reported that counter-terrorism officials in the US had issued security bulletins to police.

The Associated Press reported that one bulletin noted that an al-Qaeda training manual specifically lists "blasting and destroying the places of amusement, immorality, and sin... and attacking vital economic centers" as desired targets of the global terror network.