Five activists protesting against discussions on nuclear energy were "roughed up" at the Industrial Development Corporation (IDC) office in Sandton, Johannesburg, on Tuesday, Greenpeace Africa said.
The environmental group staged the protest in an attempt to halt talks aimed at expanding nuclear energy on the continent, spokeswoman Ferrial Adam said in a statement.
"Five Greenpeace activists have been roughed up outside the Industrial Development Corporation building in Sandton... following their action this morning where they demanded a halt to discussions aimed at expanding nuclear not only in South Africa, but also the rest of the African continent."
She said the protesters had chained themselves to the gates of the IDC when about a dozen private security guards started to "intimidate" them.
"They used their batons to break the chain and started pushing us around. Then they pulled us inside (the premises) and claimed we were trespassing," Adams said.
Greenpeace reported the matter to police, as they believed the guards used "excessive force".
Energy Minister Dipuo Peters opened the conference, which was organised by Omega Investment Research, a Cape Town-based international advisory firm.
Police could not immediately confirm the incident. - Sapa