South African intelligence sources said they believed that the US had received information that somebody with a South African passport has been flagged as being a member of ISIS, Al Shabaab or Boko Haraam. That had in turn pointed to a possible threat emanating from South Africa.

The statement – under the headline “Terrorist Threat to U.S. Interests in South Africa” – said the embassy “has received information that extremists may be targeting U.S. interests in South Africa, to possibly include U.S. Government facilities and other facilities identifiable with U.S. business interests. There is no additional information as to timing or potential targeting.

“Review your personal security plans; remain aware and vigilant of your surroundings, including local events, monitor local news stations for updates and follow instructions from local authorities,” the message warned US citizens. “Be vigilant and take appropriate steps to enhance your personal security.”

Harvey declined to elaborate on the nature of the threat. She added that the State Department had “no higher priority than the protection of US citizens overseas. Security Messages do not reflect the nature of our bilateral relations with a country. They are part of our commitment to protect US citizens travelling and residing abroad,” she added, apparently anticipating that the South African government might not like the terrorist threat warning.

“The US government, as it does in any investigation into terrorist threats against American interests around the world, will cooperate with South African authorities,” Harvey said.

She advised US citizens in South Africa to enroll their plans on www.travel.state.gov using the Smart Traveler Enrolment Progam (STEP) and to read the Country Specific Information also found on the site.

In 2009 all US embassy buildings in South Africa were shut down for three days because of an unspecified terrorist threat. South African intelligence sources said then that they had intercepted messages between members of the extremist Islamist organisation Al-Shabaab in Somalia and its agents in South Africa threatening to attack US embassy interests in revenge for the US killing one of their leaders in Somalia.

The US embassy in Pretoria and its consulates in Johannesburg, Durban and Cape Town appeared to be operating normally on Tuesday after the security message was posted.

South African intelligence sources said they could not comment yet.

On August 7, 1998, Al-Qaeda detonated two huge truck bombs at the US embassies in Nairobi and Dar-es-Salaam, killing 213 in Nairobi and 11 in Dar-es-Salaam. Though the attacks were targeted at the US, most of the dead and about 4,000 injured were locals. Twelve Americans were killed.