The sign language interpreter used at Tuesday's memorial service for Nelson Mandela was being called a "fake" by the Deaf Federation of South Africa.
The Associated Press also reported the allegation, saying that three sign language experts who watched the broadcast said the man was not signing in South African or American sign languages.
"It was horrible, an absolute circus, really really bad," Nicole Du Toit, an official sign language interpreter, told the AP. "Only he can understand those gestures."
USA TODAY was not able to confirm the allegations.
The unnamed man shared the stage with several heads of state and his signs were broadcast around the world.
South Africa's government said it is preparing a statement.