Johannesburg - South Africa has to be wary of attempts to censor the media, such as SABC COO Hlaudi Motsoeneng's recent suggestion that journalists be licensed, US ambassador Patrick Gaspard said on Tuesday.
"I was stunned that all of you weren't outside of the SABC headquarters the next morning," he said at the Nieman Society AGM in Johannesburg.
"Governments around the world are looking to control any story they can."
Motsoeneng recently suggested all journalists be licensed and that government revoke these licences should they behave unprofessionally.
Gaspard quoted journalist and writer Nat Nakasa, who died in exile in New York in 1965, saying people should speak up in a "loud and thunderous voice" should anyone or any government hint at censorship.
"Muscular vigilance" was needed to maintain press freedom, he said.
"My caution to your country and my own is too often we're neglectful of the rights that we have."
Replying to questions, Gaspard said the US government had not kept up with the pace at which technology was developing, making the leaking of state secrets more likely.
"The inability of legislature bodies to keep up with the pace of changes in technology leaves more opportunities for leaks. WikiLeaks necessarily awakened people about the capacity our governments have."
Gaspard said US President Barack Obama only resorted to using force in other countries after he had "exhausted all diplomatic tools".
He referred to the recent beheadings of two American journalists, James Foley and Steven Sotloff, by Islamic State in Iraq and Syria (Isis) militants in Syria.
Gaspard pointed out that Obama was proud of the coalition formed to pursue extremists.
"In the US, there's a sense that this kind of growth in Isis can only be slowed down with aggressive frontline activity."
Earlier, Gaspard said the relationship between South Africa and the US was still strong, despite his recent spat with Deputy Defence and Military Veterans Minister Kebby Maphatsoe. Maphatsoe had accused Public Protector Thuli Madonsela of being a CIA spy.
"Irrespective of comments made by some irresponsible people... Our relationship is still strong," he said of the two nations.