South Africa's government was accused Friday of trying to smear the ombudsman and several top opposition politicians when it announced an inquiry into allegations they were CIA spies that were based on claims of an anonymous blog.
U.S. Ambassador Patrick Gaspard dismissed the allegations as "rubbish."
"I have faith in intelligence of South Africans," said Gaspard on Twitter. "This story is a joke in any serious nation."
South African government leaders have often used law enforcement agencies to discredit their political opponents.
The government announced Thursday night that the State Security Agency was probing claims that ombudsman Thuli Madonsela, opposition figures Julius Malema and Lindiwe Mazibuko, and union leader Joseph Mathunjwa were CIA spies.
"Government has noted with great concern the allegations of espionage against the head of the Office of the Public Protector and certain political leaders in our country," Minister of State Security David Mahlobo said. "A search conducted on these allegations made, led government to the following website: africainteligenceleaks.wordpress.com, including other social media platforms."
Critics said the blog involved an anonymous figure or figures making allegations while producing no evidence.
South African activist Sisonke Msimang noted in a Tweet: "The African 'Inteligence' Blog where our secret service gets its intel, can't spell intelligence."
Madonsela, the ombudsman, last year reported that President Jacob Zuma improperly benefited from state renovations to his personal residence. Malema, a firebrand opposition leader who used to be in the governing African National Congress but was expelled, frequently attacks Zuma, calling on him to repay the money spent on his residence.
Mazibuko is a leading figure in the opposition Democratic Alliance, which controls the Western Cape and Cape Town.
The blog claimed the figures had been recruited by the CIA to discredit the country and its government.
"Is Madonsela another CIA project against South Africa or is she a CIA project against the whole African continent?" the anonymous blogger wrote, publishing several email addresses purportedly used by Madonsela.
"A grade nine pupil could see it is rubbish," Madonsela said Friday.
Malema said South Africa's biggest problem was that its intelligence agency wasn't intelligent.
"I have never heard such madness in my life," he said Friday. "Those people are clowns."
The Democratic Alliance said the CIA spies announcement was bizarre and showed how paranoid the government had become.
"It's pretty embarrassing that a South African cabinet minister would issue a press statement responding to a false blog post from the lunatic fringe," Mazibuko said.
"So here it is, all the evidence you ever needed: The government of South Africa has gone insane," wrote South African columnist Richard Poplak in the Daily Maverick.
"As the misshapen surveillance-state newborn is nursed on the government's dripping teat, we are privy to the infanthood of a true monster," he added. "But the creature will grow, and it will learn, and it will strengthen, and it will get slightly less stupid."