United States government offices in South Africa are expected to reopen on Friday after being closed for two days, reportedly after a threat from an al-Qaeda splinter group.

The Pretoria News quoted "well-placed" South African security sources on Thursday as saying the group telephoned the U.S. Embassy in Pretoria on Monday and detailed plans to attack several U.S. facilities in South Africa.

Apart from saying its decision was based on "information recently received by the regional security office," the embassy has not explained why it closed its offices on Tuesday and Wednesday of this week. (Thursday was a South African national holiday.)

Correspondents for the Pretoria News said agents from South Africa's National Intelligence Agency, its police crime intelligence unit and the South African Secret Service were working with U.S. intelligence officials to track down those behind the threat.

"A security source within the intelligence field said the calls, believed to have come from South Africa, had been intercepted by U.S. intelligence agencies," the paper reported.

The embassy published a notice on Thursday recording "its appreciation to the South African Government, and in particular the South African Police Service (SAPS) Division: Crime Intelligence, for outstanding cooperation and support."

In Cape Town, authorities closed a private school in the vicinity of a recently-built U.S. embassy building, which was relocated from downtown Cape Town to the outskirts of the city.